I was encountering the same problem. I solved it for myself through trial-and-error.
In my case, it was related to an extension, “Privacy Badger”, blocking access to some endpoint needed for the new WebSocket implementation OpenAI rolled out recently to Chromium-based desktop browsers. Privacy Badger extension wasn’t allowing access to endpoints required by the recent changes OpenAI made on the backend.
It was impacting Google Chrome Dev, Brave, and Microsoft Edge Dev, in my case. I did not test other browsers. But this making the change in the 2nd image below solved the issue for all three browsers.
See below for the problematic settings and the settings that fixed it, respectively. Note, these settings were seen while clicking the extension while actively logged in on the chat.openai.com website.
Image 1 (Privacy Badger settings that were causing problems):
Image 2 (Privacy Badger settings that fixed the issue):
I doubt that this will fix the problem for all users in all cases. There are likely other scenarios that trigger this error.
However, it might be worth trying this fix for users that have the Privacy Badger extension enabled.