I can confirm having the same issue with Firefox on Linux. I am pursuing it with OpenAI support. They keep on asking me for stuff, but have not yet acknowledged whether they can recreate it. It is likely there are is some specific network path trigger for it. I tried with and without STUN.
There was this old forum item that was closed (not mine) that has many more details
And this one
I hope @OpenAI_Support can invest some time into testing/recreating, as there are many different reports, and a bug on the mozilla bugtracker suggesting that it is non-standards based behaviour of the OpenAI backend. The Mozilla ticket suggests they were trying to get hold of somebody in OpenAI in the appropriate team, but that person moved on