Strange delays in websocket data transfer from Ubuntu-hosted wifi access point

Question

I have an application that is streaming jpeg images from an Ubuntu machine over a wifi connection. The wifi network is an access point/SSID hosted on the Ubuntu machine that is streaming the images. I have run this in two scenarios, with very different results. In the first, I set up the wifi AP using an nmcli-driven script I wrote long ago. This gave me acceptable performance: just under 200 ms to transfer a ~500kb image over a websocket. We then changed the way the AP network was set up using nmtui. When the AP was set up this way, the performance got noticeably worse: the 500k jpeg now takes ~800ms to transfer. And, once this problem manifested, going back to instantiating the AP using the old script didn't help: the transfer time stayed stubbornly at ~800 ms. From this I conclude that some system level network setting got turned on/off in the process of using nmtui to instantiate the access point.

My question is this... Is there some setting (in linux or elsewhere) that could cause this? I was imagining something like a different setting on the size of the network send buffer, or some checksum process that runs every 12k bytes or so, or something similar. Might that be the problem? Or am I looking in the wrong place entirely?

More information: the wireshark view of the transfer (from the point of view of the laptop receiving the images) is interesting. Here are the first several packet fragments in the original (fast) configuration:

No.	Time	Source	Destination	Protocol	Length	Info	Time between TCP segments
3021	42.848808	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Binary [TCP segment of a reassembled PDU]
3024	42.848808	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0
3029	42.850256	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.001448
3033	42.853634	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.003378
3037	42.854018	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.000384
3040	42.85586	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.001842
3044	42.858978	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.003118
3047	42.858978	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0
3051	42.859479	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.000501
3056	42.863421	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.003942
3058	42.863421	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0
3062	42.867284	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.003863
3065	42.867284	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0
3069	42.869294	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.00201
3073	42.870653	192.168.5.1	192.168.5.175	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.001359

Compare that with the slower version:

No.	Time	Source	Destination	Protocol	Length	Info	Time between packet fragments
2300	47.71488	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Binary [TCP segment of a reassembled PDU]
2304	47.716615	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.001735
2309	47.722165	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.00555
2313	47.724079	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.001914
2318	47.728149	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.00407
2321	47.730169	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.00202
2325	47.732195	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.002026
2330	47.736405	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.00421
2334	47.763687	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.027282
2339	47.768259	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.004572
2342	47.773175	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.004916
2346	47.775568	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.002393
2351	47.779664	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.004096
2355	47.782844	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.00318
2360	47.78672	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.003876
2363	47.788629	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.001909
2367	47.815898	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.027269
2372	47.819907	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.004009
2376	47.823592	10.0.2.1	10.0.2.198	WebSocket	1514	WebSocket Continuation [TCP segment of a reassembled PDU]	0.003685

Notice that, in the slower version, there is a much longer time gap (highlighted in bold) between TCP fragments occurring every ~12k bytes or so. (That is consistent- there is a big lag between fragments at predictable intervals in this scenario).