debug Apk works fine but playstore apk crashes repeatedly

Question

I had developed an update (with flutter) for my existing app in playstore. All went well so uploaded to playstore signing with my old key. (Ref:https://docs.flutter.dev/deployment/android)

CASE1: After google review when i downloaded the app from playstore, the app crashes.

java.lang.RuntimeException: at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:3718) at android.app.ActivityThread.handleLaunchActivity (ActivityThread.java:4003) at android.app.servertransaction.LaunchActivityItem.execute (LaunchActivityItem.java:85) at android.app.servertransaction.TransactionExecutor.executeCallbacks (TransactionExecutor.java:135) at android.app.servertransaction.TransactionExecutor.execute (TransactionExecutor.java:95) at android.app.ActivityThread$H.handleMessage (ActivityThread.java:2317) at android.os.Handler.dispatchMessage (Handler.java:106) at android.os.Looper.loop (Looper.java:246) at android.app.ActivityThread.main (ActivityThread.java:8595) at java.lang.reflect.Method.invoke (Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:602) at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1130) Caused by: java.lang.ClassNotFoundException:
at dalvik.system.BaseDexClassLoader.findClass (BaseDexClassLoader.java:207) at java.lang.ClassLoader.loadClass (ClassLoader.java:379) at java.lang.ClassLoader.loadClass (ClassLoader.java:312) at android.app.AppComponentFactory.instantiateActivity (AppComponentFactory.java:95) at androidx.core.app.CoreComponentFactory.instantiateActivity (Unknown Source) at android.app.Instrumentation.newActivity (Instrumentation.java:1253) at android.app.ActivityThread.performLaunchActivity (ActivityThread.java:3706)

Case 2: So i tried to run the same apk in mobile device which resulted in follwing error.

I followed the suggestions from stack-thread to desable the play protect and run it again, but its not getting installed.

I had already asked google to update my key. but would like to know of any alternative solutions.