I experienced exactly the same thing since I upgraded to Pro (a week ago) and I was never able to get a solution, I don’t think it happens on all accounts as otherwise it would be more widespread but I gave up trying to use Pro temporarily, the results I had using o1 with Plus were much better than o1 on this plan.
There are some posts about it, but they didn’t have much impact:
After a week of trying in vain to get support to analyze the case, I could never understand why things that I see others doing with o1 Pro (even replicating steps I see in Youtube reviews), in my case they behave differently, which somewhat supports my hypothesis that it is a particular problem with some accounts, but anyway as I said, I never even managed to make any real progress with support, they just don’t care.