Lost (offline) save after connecting to microsoft account

I played offline until my hero reached level 6, then decided to sign in to my Microsoft account. On the first attempt, I got an error message saying the account couldn't be connected, so I restarted the game. After the restart, the game successfully connected to my Microsoft account but then immediately crashed. When I reopened the game, my hero had been reset to level 1. I also tried restoring an older save backup through the Nintendo Switch, but that didn't recover my progress.