Yeah, I have the exact same problem. I was stuck in round 3 of gauntlet. If i won the game did not count and kicked me out of UT. I was able to re-enter the mode. Sometimes during the 3rd game I would get disconnected and the game would count as being not played regardless of the score. Today I went into the mode and decided to test closing the app hoping that would end my current gauntlet entry and allow me to start a new one. Now i am locked out of UT, the web and companion app both fail to log in as they say I am signed in on another device.
Also i am on ps5 and i have tested clearing the system cache, rebuilding the database, I have used my phone's hotspot instead of my wifi all of these have not fixed the issue. I have managed to log in to ultimate team on my second account however which did not have an ultimate team created. This shows that it is not an internet connection or console issue this is an issue isolated to specific EA accounts.
I have spoken with an EA representative who claims they have made notes about this case and similar cases and asked me to keep an eye on twitter/X for any updates. They claim they are aware but please push this post to make sure they are aware of this account specific bug.
Other modes continue to work at the moment however, no clue if they will also be affected.