macOS desktop Chat progressively stalls after recent update while Web and Codex remain responsive

What version of the Codex App are you using (From “About Codex” dialog)?

26.908.40834

What subscription do you have?

ChatGPT Plus

What platform is your computer?

Darwin 23.6.0 arm64 arm

What issue are you seeing?

Environment
macOS desktop app
Issue started after a recent desktop app update
ChatGPT Web works normally on the same Mac/account/network
Codex tasks inside the desktop app remain responsive
Symptoms
Immediately after restarting the app, the first 1–2 Chat turns are usually fast.
After a few turns, message submission starts spinning for 20–60+ seconds.
After submission succeeds, generation may stall before the first token appears.
The delay becomes progressively worse over time.
If I launch the app and leave it idle for a while before chatting, Chat can already be very slow.
Eventually the app may show timeout or net::ERR_HTTP2_PING_FAILED.
Restarting the app immediately restores normal Chat performance, but the problem returns again.
Restarting only the app’s NetworkService process also temporarily restores Chat, but interrupts Codex.
At times, push notifications for new Chat replies still arrive even while the desktop app cannot load the corresponding conversation.
Codex usage/quota display can also become stale while Chat is stalled and refresh only after restarting the app.
Network observations
The app uses a local HTTP/PAC proxy.
During the failure, NetworkService still has multiple established TCP connections to the local proxy.
A NetLog captured during reproduction shows successful proxy CONNECT establishment to ws.chatgpt.com.
The NetLog also contains HTTP/2 protocol errors / stream resets.
Disabling HTTP/2 and QUIC did not resolve the issue.
Resetting Chromium network state files did not resolve it.
Expected behavior
Chat in the desktop app should remain responsive over time, as it did before the recent update and as ChatGPT Web still does.
Privacy
I am not attaching the raw NetLog publicly because it may contain account identifiers or other sensitive metadata. I can provide sanitized excerpts if needed.
This appears to be a regression in the desktop Chat networking path rather than a general connectivity issue, because Web and Codex remain responsive while Chat progressively degrades.

What steps can reproduce the bug?

Launch the latest ChatGPT macOS desktop app.
Open any normal Chat conversation.
Send one or two messages shortly after launch — these are usually fast.
Continue chatting for a few more turns, or leave the app idle for several minutes before sending another message.
Message submission then starts spinning for 20–60+ seconds.
After submission succeeds, generation may remain stuck before the first token appears.
The delay becomes progressively worse with subsequent turns.
Eventually the app may show a timeout or net::ERR_HTTP2_PING_FAILED.
Restarting the desktop app immediately restores normal Chat performance for a short time, after which the same degradation repeats.
Additional observations:
ChatGPT Web works normally on the same Mac/account/network.
Codex tasks inside the desktop app remain responsive while normal Chat is stalling.
Restarting only the app’s NetworkService process temporarily restores Chat, but also interrupts Codex.

What is the expected behavior?

Chat in the macOS desktop app should remain responsive over time and after being idle, without progressively increasing submission/generation delays or requiring the app to be restarted.

Additional information

No response

Reproduce the degradation in the macOS desktop app using the listed message sequence, then inspect NetworkService behavior and a sanitized NetLog around the HTTP/2 stream resets and proxy connections. Compare Chat with Web and Codex, and verify that Chat remains responsive after repeated turns and idle time without restarting the app or NetworkService.