Updated to AI 2026, and now I'm locked out of numerous files :-(

I upgraded to Illustrator 2026 yesterday, and today it's telling me it can't open many of my files because "the account you signed in with doesn't have access to this file. Contact the owner for more info."

What?? I'm the owner....I didn't create a new account...what is going on?? Somebody please help, I'm locked out of so many important files. 😭