Hey dhaker_wolf,
If you are running into an error starting a Rivals or Champions match, it could be related to an EVO applied to one or more of your players that granted a 5th PlayStyle+ that's not working correctly. Removing or replacing the EVO should help.
Other players also reported this situation recently, and our teams are investigating.
In the meantime, if you also run into an error submitting an SBC, is it a single SBC or any SBC you're trying to submit? If you have submitted many SBCs before this error started, please try taking a 24-hour break from attempting to submit new SBCs. You might have been targeted by our security systems against bots and automations.
For the Gauntlet mode instead, please check if you can start a match without editing your squad.
It might also help to delete the corrupt files following this guide, including the Online squad updates and Personal settings 1 files, and to delete your squads on the Companion app or the Web app, leaving an empty one as the active squad, before you try to start a new match in-game.
Let me know how it goes.