react-native app starting up slowly (ios)

Question

I have a react-native app which is starting up very slowly on IOS (both on simulator and real device). It happens with both the debug build and the release build. It takes up to 8 seconds in the release build before the bootsplash fades away and the home screen pops up. Checking the xcode log, it seems that nothing is happening in the app, because during this period, I don't get any output.

This is the xcode log output I get from a startup on a real device. I have added a box where the app 'waits' for 5 seconds.

What I tried so far:

• disabling and deleting all firebase modules (not working)
• disabling and deleting react-native-ffmpeg (not working)
• adding environment variable "OS_ACTIVITY_MODE" (disable) to my scheme, but this doesn't give me any output (not working)

I have the following arguments passed on launch:

• -FIRAnalyticsDebugEnabled
• -FIRDebugEnabled
• -FIRAnalyticsDebugEnabled

Could it be a performance issue? Maybe I don't have enough memory or it hits the memory limit on start up (I'm guessing here because I really don't know). My app is rather simple and is not very big in size. If someone could tell me how to monitor the performance (if this is the issue).

2021-03-11 19:41:48.008493+0100 myapp[51053:3251312] [Firebase/Crashlytics] Version 7.6.0
2021-03-11 19:41:48.060959+0100 myapp[51053:3251312] +[RNFBCrashlyticsInitProvider isCrashlyticsCollectionEnabled] [Line 41] isCrashlyticsCollectionEnabled via RNFBPreferences: 1
2021-03-11 19:41:48.061037+0100 myapp[51053:3251312] +[RNFBCrashlyticsInitProvider isCrashlyticsCollectionEnabled] [Line 51] isCrashlyticsCollectionEnabled: 1
2021-03-11 19:41:48.061110+0100 myapp[51053:3251312] +[RNFBCrashlyticsInitProvider configureWithApp:] [Line 92] initialization successful
2021-03-11 19:41:48.097352+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Core][I-COR000003] The default Firebase app has not yet been configured. Add `[FIRApp configure];` (`FirebaseApp.configure()` in Swift) to your application initialization. Read more: URL.
2021-03-11 19:41:48.142784+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Core][I-COR000001] Configuring the default app.
2021-03-11 19:41:48.143085+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Core][I-COR000033] Data Collection flag is not set.
2021-03-11 19:41:48.143340+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Installations][I-FIS002000] -[FIRInstallationsIDController createGetInstallationItemPromise], appName: __FIRAPP_DEFAULT
2021-03-11 19:41:48.148896+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Crashlytics][I-CLS000000] [Crashlytics] Running on iPhone8,1, 14.4.0 (18D52)
2021-03-11 19:41:48.149222+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Crashlytics][I-CLS000000] [Crashlytics:Settings] No settings were cached
2021-03-11 19:41:48.149462+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Crashlytics][I-CLS000000] Root: /var/mobile/Containers/Data/Application/EF0DCE91-3A1E-435C-A100-66EC71D229CC/Library/Caches/com.crashlytics.data/com.myappized.myapp
2021-03-11 19:41:48.149787+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Crashlytics][I-CLS000000] [Crashlytics:Crash:Reports:Event] Registered Firebase Analytics event listener to receive breadcrumb logs
2021-03-11 19:41:48.150074+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Crashlytics][I-CLS000000] Automatic data collection is enabled.
2021-03-11 19:41:48.150281+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Crashlytics][I-CLS000000] Unsent reports will be uploaded at startup
2021-03-11 19:41:48.150487+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Messaging][I-FCM002000] FIRMessaging library version 7.6.0
2021-03-11 19:41:48.150694+0100 myapp[51053:3251509] 7.6.0 - [GULReachability][I-REA902003] Monitoring the network status
2021-03-11 19:41:48.151059+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Messaging][I-FCM001000] FIRMessaging Remote Notifications proxy enabled, will swizzle remote notification receiver handlers. If you'd prefer to manually integrate Firebase Messaging, add "FirebaseAppDelegateProxyEnabled" to your Info.plist, and set it to NO. Follow the instructions at:
https://firebase.google.com/docs/cloud-messaging/ios/client#method_swizzling_in_firebase_messaging
to ensure proper integration.
2021-03-11 19:41:48.151897+0100 myapp[51053:3251509] 7.6.0 - [GoogleUtilities/AppDelegateSwizzler][I-SWZ001008] Successfully created App Delegate Proxy automatically. To disable the proxy, set the flag GoogleUtilitiesAppDelegateProxyEnabled to NO (Boolean) in the Info.plist
2021-03-11 19:41:48.165066+0100 myapp[51053:3251495] 7.6.0 - [GULReachability][I-REA902003] Monitoring the network status
2021-03-11 19:41:48.165541+0100 myapp[51053:3251495] 7.6.0 - [GULReachability][I-REA902003] Monitoring the network status
2021-03-11 19:41:48.168557+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS024000] Debug mode is on
2021-03-11 19:41:48.168876+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS005000] The AdSupport Framework is not currently linked. Some features will not function properly. Learn more at URL
2021-03-11 19:41:48.169343+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS023007] Analytics v.7.6.0 started
2021-03-11 19:41:48.169871+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS023008] To disable debug logging set the following application argument: -noFIRAnalyticsDebugEnabled (see URL)
2021-03-11 19:41:48.170405+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS023009] Debug logging enabled
2021-03-11 19:41:48.170621+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS023207] To enable verbose logging set the following application argument: -FIRAnalyticsVerboseLoggingEnabled (see URL)
2021-03-11 19:41:48.181301+0100 myapp[51053:3251504] 7.6.0 - [Firebase/Analytics][I-ACS002002] APMExperimentAlarm scheduled to fire in approx. (s): 13086.19100010395
2021-03-11 19:41:48.181793+0100 myapp[51053:3251504] 7.6.0 - [Firebase/Analytics][I-ACS800023] No pending snapshot to activate. SDK name: app_measurement
2021-03-11 19:41:48.182454+0100 myapp[51053:3251504] 7.6.0 - [Firebase/Analytics][I-ACS029014] Successfully parsed a configuration. Version: 1613040234009562
2021-03-11 19:41:48.182670+0100 myapp[51053:3251504] 7.6.0 - [Firebase/Analytics][I-ACS023016] Analytics is ready to receive events
2021-03-11 19:41:48.190708+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS032003] iAd framework is not linked. Search Ad Attribution Reporter is disabled.
2021-03-11 19:41:48.191335+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS023012] Analytics collection enabled
2021-03-11 19:41:48.191948+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS023220] Analytics screen reporting is enabled. Call +[FIRAnalytics logEventWithName:FIREventScreenView parameters:] to log a screen view event. To disable automatic screen reporting, set the flag FirebaseAutomaticScreenReportingEnabled to NO (boolean) in the Info.plist
2021-03-11 19:41:48.261752+0100 myapp[51053:3251312] [native] Running application myapp ({
    initialProps =     {
        isHeadless = 0;
    };
    rootTag = 1;
})
2021-03-11 19:41:48.386230+0100 myapp[51053:3251507] 7.6.0 - [GULReachability][I-REA902004] Network status has changed. Code:2, status:Connected
2021-03-11 19:41:48.386675+0100 myapp[51053:3251507] 7.6.0 - [GULReachability][I-REA902004] Network status has changed. Code:1, status:Disconnected
2021-03-11 19:41:48.386953+0100 myapp[51053:3251507] 7.6.0 - [GULReachability][I-REA902004] Network status has changed. Code:2, status:Connected
2021-03-11 19:41:48.387197+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Crashlytics][I-CLS000000] Failed to download settings. If this is your first time launching the app, make sure you have enabled Crashlytics in the Firebase Console. Error Domain=FIRCLSNetworkError Code=-5 "(null)" UserInfo={status_code=404, type=2, request_id=, content_type=text/html; charset=utf-8}
2021-03-11 19:41:48.387724+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS002002] Engagement timer scheduled to fire in approx. (s): 3600
2021-03-11 19:41:48.387978+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS031010] Tracking view controller. Class, ID: UIViewController, 8672806308884068698
2021-03-11 19:41:48.391668+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Analytics][I-ACS023051] Logging event: origin, name, params: auto, screen_view (_vs), {
    ga_event_origin (_o) = auto;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068698;
}
2021-03-11 19:41:48.391709+0100 myapp[51053:3251509] 7.6.0 - [Firebase/Analytics][I-ACS023073] Debug mode is enabled. Marking event as debug and real-time. Event name, parameters: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068698;
}
2021-03-11 19:41:48.454534+0100 myapp[51053:3251507] 7.6.0 - [Firebase/InstanceID][I-IID003012] Provisioning profile has specifically provisioned devices, most likely a Dev profile.
2021-03-11 19:41:48.454582+0100 myapp[51053:3251507] 7.6.0 - [Firebase/InstanceID][I-IID003013] APNS Environment in profile: development
2021-03-11 19:41:48.454721+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Installations][I-FIS002001] -[FIRInstallationsIDController installationWithValidAuthTokenForcingRefresh:0], appName: __FIRAPP_DEFAULT
2021-03-11 19:41:48.455179+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS031010] Tracking view controller. Class, ID: UIViewController, 8672806308884068699
2021-03-11 19:41:48.455335+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS031006] View controller already tracked. Class, ID: UIViewController, 8672806308884068699
2021-03-11 19:41:48.455440+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS031006] View controller already tracked. Class, ID: UIViewController, 8672806308884068699
2021-03-11 19:41:48.458361+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS023072] Event logged. Event name, event params: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068698;
}
2021-03-11 19:41:48.467557+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS002002] Measurement timer scheduled to fire in approx. (s): 0.8769718408584595
2021-03-11 19:41:48.468256+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS023051] Logging event: origin, name, params: auto, screen_view (_vs), {
    ga_event_origin (_o) = auto;
    ga_previous_class (_pc) = UIViewController;
    ga_previous_id (_pi) = 8672806308884068698;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068699;
}
2021-03-11 19:41:48.476723+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS023073] Debug mode is enabled. Marking event as debug and real-time. Event name, parameters: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_previous_class (_pc) = UIViewController;
    ga_previous_id (_pi) = 8672806308884068698;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068699;
}
2021-03-11 19:41:48.479961+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS023072] Event logged. Event name, event params: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_previous_class (_pc) = UIViewController;
    ga_previous_id (_pi) = 8672806308884068698;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068699;
}
2021-03-11 19:41:49.382664+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS002001] Measurement timer fired
2021-03-11 19:41:49.384057+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS002003] Measurement timer canceled
2021-03-11 19:41:49.388408+0100 myapp[51053:3251510] 7.6.0 - [Firebase/Analytics][I-ACS023105] Event is not subject to real-time event count daily limit. Marking an event as real-time. Event name, parameters: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068698;
}
2021-03-11 19:41:49.396836+0100 myapp[51053:3251510] 7.6.0 - [Firebase/Analytics][I-ACS012018] Saving bundle. size (bytes): 444
2021-03-11 19:41:49.397547+0100 myapp[51053:3251510] 7.6.0 - [Firebase/Analytics][I-ACS023116] Bundle added to the upload queue. BundleID, timestamp (ms): 767, 1615488108344
2021-03-11 19:41:49.414154+0100 myapp[51053:3251510] 7.6.0 - [Firebase/Analytics][I-ACS023105] Event is not subject to real-time event count daily limit. Marking an event as real-time. Event name, parameters: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_previous_class (_pc) = UIViewController;
    ga_previous_id (_pi) = 8672806308884068698;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068699;
}
2021-03-11 19:41:49.422186+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS012018] Saving bundle. size (bytes): 479
2021-03-11 19:41:49.422982+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS023116] Bundle added to the upload queue. BundleID, timestamp (ms): 768, 1615488108439
2021-03-11 19:41:49.435764+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS023039] Measurement data sent to network. Timestamp (ms), data: 1615488109435, <APMPBMeasurementBatch: 0x2815d4930>
2021-03-11 19:41:49.446537+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS900000] Uploading data. Host: https://app-measurement.com/a
2021-03-11 19:41:49.599200+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS901006] Received SSL challenge for host. Host: https://app-measurement.com/a
2021-03-11 19:41:49.674735+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS023044] Successful upload. Got network response. Code, size: 204, -1
2021-03-11 19:41:49.677836+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS002002] Measurement timer scheduled to fire in approx. (s): -0.2385810613632202
2021-03-11 19:41:49.696110+0100 myapp[51053:3251495] 7.6.0 - [Firebase/Analytics][I-ACS002003] Measurement timer canceled
2021-03-11 19:41:52.130340+0100 myapp[51053:3251507] [connection] nw_socket_handle_socket_event [C8:1] Socket SO_ERROR [61: Connection refused]
2021-03-11 19:41:52.131384+0100 myapp[51053:3251518] [connection] nw_connection_get_connected_socket [C8] Client called nw_connection_get_connected_socket on unconnected nw_connection
2021-03-11 19:41:52.131447+0100 myapp[51053:3251518] TCP Conn 0x2820ca940 Failed : error 0:61 [61]
2021-03-11 19:41:52.143572+0100 myapp[51053:3251515] [javascript] Loading react-native-ffmpeg.
2021-03-11 19:41:52.345864+0100 myapp[51053:3251515] +[RNFBCrashlyticsInitProvider isCrashlyticsCollectionEnabled] [Line 41] isCrashlyticsCollectionEnabled via RNFBPreferences: 1
2021-03-11 19:41:52.346040+0100 myapp[51053:3251515] +[RNFBCrashlyticsInitProvider isCrashlyticsCollectionEnabled] [Line 51] isCrashlyticsCollectionEnabled: 1
2021-03-11 19:41:52.346133+0100 myapp[51053:3251515] +[RNFBCrashlyticsInitProvider isErrorGenerationOnJSCrashEnabled] [Line 68] isErrorGenerationOnJSCrashEnabled via RNFBMeta: 1
2021-03-11 19:41:52.346172+0100 myapp[51053:3251515] +[RNFBCrashlyticsInitProvider isErrorGenerationOnJSCrashEnabled] [Line 71] isErrorGenerationOnJSCrashEnabled: 1
2021-03-11 19:41:52.360074+0100 myapp[51053:3251507] Loaded mobile-ffmpeg-full-arm64-4.4-20200725
2021-03-11 19:41:52.376855+0100 myapp[51053:3251515] [javascript] Reactotron Configured
2021-03-11 19:41:52.381267+0100 myapp[51053:3251515] [javascript] Running "myapp" with {"rootTag":1,"initialProps":{"isHeadless":false}}
2021-03-11 19:41:52.424426+0100 myapp[51053:3251515] [javascript] Loaded react-native-ffmpeg-ios-arm64.
2021-03-11 19:41:52.636578+0100 myapp[51053:3251518] [connection] nw_socket_handle_socket_event [C9:1] Socket SO_ERROR [61: Connection refused]
2021-03-11 19:41:52.637578+0100 myapp[51053:3251507] [connection] nw_connection_get_connected_socket [C9] Client called nw_connection_get_connected_socket on unconnected nw_connection
2021-03-11 19:41:52.643628+0100 myapp[51053:3251507] TCP Conn 0x2820ca5d0 Failed : error 0:61 [61]
2021-03-11 19:41:52.650326+0100 myapp[51053:3251507] 7.6.0 - [Firebase/Analytics][I-ACS031006] View controller already tracked. Class, ID: UIViewController, 8672806308884068699
+------------------------------------+
|                                    |
|                                    |
| the app 'waits' for 5 seconds here |
|                                    |
|                                    |
+------------------------------------+
2021-03-11 19:41:57.566089+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS023012] Analytics collection enabled
2021-03-11 19:41:57.567127+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS023220] Analytics screen reporting is enabled. Call +[FIRAnalytics logEventWithName:FIREventScreenView parameters:] to log a screen view event. To disable automatic screen reporting, set the flag FirebaseAutomaticScreenReportingEnabled to NO (boolean) in the Info.plist
2021-03-11 19:41:58.299157+0100 myapp[51053:3251312] [native] [GESTURE HANDLER] Initialize gesture handler for root view <RCTRootContentView: 0x1076250a0; reactTag: 1; frame = (0 0; 375 667); gestureRecognizers = <NSArray: 0x2819b6850>; layer = <CALayer: 0x2817f82c0>>
2021-03-11 19:41:59.105297+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS031029] Logging screen view with screen name and screen class: Authentication, Authentication
2021-03-11 19:41:59.105849+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS002003] Engagement timer canceled
2021-03-11 19:41:59.106139+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS002002] Engagement timer scheduled to fire in approx. (s): 3600
2021-03-11 19:41:59.108370+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS023051] Logging event: origin, name, params: auto, user_engagement (_e), {
    engagement_time_msec (_et) = 10794;
    ga_event_origin (_o) = auto;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068699;
}
2021-03-11 19:41:59.110672+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS023073] Debug mode is enabled. Marking event as debug and real-time. Event name, parameters: user_engagement (_e), {
    engagement_time_msec (_et) = 10794;
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068699;
}
2021-03-11 19:41:59.120280+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS023072] Event logged. Event name, event params: user_engagement (_e), {
    engagement_time_msec (_et) = 10794;
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068699;
}
2021-03-11 19:41:59.133726+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS002002] Measurement timer scheduled to fire in approx. (s): 0.542557954788208
2021-03-11 19:41:59.134305+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS023051] Logging event: origin, name, params: app, screen_view (_vs), {
    ga_event_origin (_o) = app;
    ga_previous_class (_pc) = UIViewController;
    ga_previous_id (_pi) = 8672806308884068699;
    ga_screen (_sn) = Authentication;
    ga_screen_class (_sc) = Authentication;
    ga_screen_id (_si) = 8672806308884068700;
}
2021-03-11 19:41:59.134853+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS023073] Debug mode is enabled. Marking event as debug and real-time. Event name, parameters: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = app;
    ga_previous_class (_pc) = UIViewController;
    ga_previous_id (_pi) = 8672806308884068699;
    ga_realtime (_r) = 1;
    ga_screen (_sn) = Authentication;
    ga_screen_class (_sc) = Authentication;
    ga_screen_id (_si) = 8672806308884068700;
}
2021-03-11 19:41:59.139822+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS023072] Event logged. Event name, event params: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = app;
    ga_previous_class (_pc) = UIViewController;
    ga_previous_id (_pi) = 8672806308884068699;
    ga_realtime (_r) = 1;
    ga_screen (_sn) = Authentication;
    ga_screen_class (_sc) = Authentication;
    ga_screen_id (_si) = 8672806308884068700;
}
2021-03-11 19:41:59.145785+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS002003] Measurement timer canceled
2021-03-11 19:41:59.148321+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS002002] Measurement timer scheduled to fire in approx. (s): 0.5287199020385742
2021-03-11 19:41:59.394825+0100 myapp[51053:3251562] 7.6.0 - [Firebase/Analytics][I-ACS031010] Tracking view controller. Class, ID: UIViewController, 8672806308884068701
2021-03-11 19:41:59.397475+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS023051] Logging event: origin, name, params: auto, screen_view (_vs), {
    ga_event_origin (_o) = auto;
    ga_previous_class (_pc) = Authentication;
    ga_previous_id (_pi) = 8672806308884068700;
    ga_previous_screen (_pn) = Authentication;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068701;
}
2021-03-11 19:41:59.398044+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS023073] Debug mode is enabled. Marking event as debug and real-time. Event name, parameters: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_previous_class (_pc) = Authentication;
    ga_previous_id (_pi) = 8672806308884068700;
    ga_previous_screen (_pn) = Authentication;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068701;
}
2021-03-11 19:41:59.403021+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS023072] Event logged. Event name, event params: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_previous_class (_pc) = Authentication;
    ga_previous_id (_pi) = 8672806308884068700;
    ga_previous_screen (_pn) = Authentication;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068701;
}
2021-03-11 19:41:59.413938+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS002003] Measurement timer canceled
2021-03-11 19:41:59.414350+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS002002] Measurement timer scheduled to fire in approx. (s): 0.2607929706573486
2021-03-11 19:41:59.675053+0100 myapp[51053:3251508] 7.6.0 - [Firebase/Analytics][I-ACS002001] Measurement timer fired
2021-03-11 19:41:59.675431+0100 myapp[51053:3251508] 7.6.0 - [Firebase/Analytics][I-ACS002003] Measurement timer canceled
2021-03-11 19:41:59.676922+0100 myapp[51053:3251508] 7.6.0 - [Firebase/Analytics][I-ACS023105] Event is not subject to real-time event count daily limit. Marking an event as real-time. Event name, parameters: user_engagement (_e), {
    engagement_time_msec (_et) = 10794;
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068699;
}
2021-03-11 19:41:59.677583+0100 myapp[51053:3251508] 7.6.0 - [Firebase/Analytics][I-ACS023105] Event is not subject to real-time event count daily limit. Marking an event as real-time. Event name, parameters: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = app;
    ga_previous_class (_pc) = UIViewController;
    ga_previous_id (_pi) = 8672806308884068699;
    ga_realtime (_r) = 1;
    ga_screen (_sn) = Authentication;
    ga_screen_class (_sc) = Authentication;
    ga_screen_id (_si) = 8672806308884068700;
}
2021-03-11 19:41:59.678471+0100 myapp[51053:3251508] 7.6.0 - [Firebase/Analytics][I-ACS023105] Event is not subject to real-time event count daily limit. Marking an event as real-time. Event name, parameters: screen_view (_vs), {
    ga_debug (_dbg) = 1;
    ga_event_origin (_o) = auto;
    ga_previous_class (_pc) = Authentication;
    ga_previous_id (_pi) = 8672806308884068700;
    ga_previous_screen (_pn) = Authentication;
    ga_realtime (_r) = 1;
    ga_screen_class (_sc) = UIViewController;
    ga_screen_id (_si) = 8672806308884068701;
}
2021-03-11 19:41:59.684894+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS023087] User property set. Name, value: lifetime_user_engagement (_lte), 11931600
2021-03-11 19:41:59.685329+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS023087] User property set. Name, value: session_user_engagement (_se), 420648
2021-03-11 19:41:59.687091+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS012018] Saving bundle. size (bytes): 580
2021-03-11 19:41:59.687189+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS023116] Bundle added to the upload queue. BundleID, timestamp (ms): 769, 1615488119391
2021-03-11 19:41:59.701620+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS023039] Measurement data sent to network. Timestamp (ms), data: 1615488119701, <APMPBMeasurementBatch: 0x2815f9160>
2021-03-11 19:41:59.704328+0100 myapp[51053:3251510] 7.6.0 - [Firebase/Analytics][I-ACS900000] Uploading data. Host: https://app-measurement.com/a
2021-03-11 19:41:59.751823+0100 myapp[51053:3251506] 7.6.0 - [Firebase/Analytics][I-ACS901006] Received SSL challenge for host. Host: https://app-measurement.com/a
2021-03-11 19:41:59.798842+0100 myapp[51053:3251508] 7.6.0 - [Firebase/Analytics][I-ACS023044] Successful upload. Got network response. Code, size: 204, -1
2021-03-11 19:41:59.801844+0100 myapp[51053:3251508] 7.6.0 - [Firebase/Analytics][I-ACS002002] Measurement timer scheduled to fire in approx. (s): 0.5894370079040527
2021-03-11 19:41:59.818817+0100 myapp[51053:3251510] 7.6.0 - [Firebase/Analytics][I-ACS002003] Measurement timer canceled

Edit:

I've checked some stats with xcode instruments.

1. Activity: everything seems normal, thermal state stays normal. During the period when the app is 'doing nothing' (the 5 seconds where the app is still in launch mode and the bootsplash screen is still shown), the CPU total load goes up to +150%. When the app finally launches, it drops back to 35%.
2. Leaks: no leaks detected on startup.

Answer 1

Looks like you accidentally turn on slow animation. Try to check that settings