Hey Alilocsc,
Please go to the Companion app or the Web app, delete your active squad, set up a new empty active squad there, then wait a couple of minutes and try to access UT again on your platform. Refreshing the squad data on the apps should resolve the UT access error.
To try and avoid further problems during the Gauntlet, I'd also recommend you try to play a new Gauntlet session all at once, without backing out of the mode, changing the squad, or playing in different modes in between Gauntlet matches.
If you could also record your new Gauntlet session and share the video with us, in case the same disconnections at the end of a match persist; it might help us identify what could be causing it.