I used the same Gamertag: ARoweToeToToe on both my PC and Switch.  I played both in solo play until today.  I went back and forth between them several times and even logged in on one while the other was active.  All it would do is log the other one out and give a disconnect pop up.

Today I played in a game online on my PC.  My friend was hosting, I joined his game.  We played for a couple hours.  I went back to my Switch and the game gets to the 'Press Any Key' screen.  I press a button.  It does the auto save ring in the lower right for several seconds while the red block rotates.  The autosave ring goes away, but the red block keeps rotating forever.  I've waited 10+ minutes.

My PC version works fine (that I'm aware of) and I can create new profiles on my switch that aren't associated with my Gamertag that can play.  I can't access my original Switch character at all.  I'm on Windows 10 for my PC.

The game is amazing, thank you for your patience