Instinct stopped syncing with Garmin Explore (after forced downgrade from Beta to PROD Software 7.20)

My Instinct stopped syncing with Garmin Explore (Garmin Connect still works). Specifically, it gets stuck at "Syncing Waypoints", then after a few minutes says "Sync failed".

This is happening, since I was forcefully downgraded from the latest Garmin Beta to PROD Software 7.20 (which also wiped all my settings).

I already deleted all waypoints in Explore, as well as on the watch. I also master-reset the watch, reinstalled Software 7.20 once again, Updated to the latest Beta once again. Reconnected the watch multiple times with both Garmin Connect and Explore. But whatever I do, I still always get stuck at "Syncing Waypoints". Something got seriously messed up.

I'm really lost on how to solve this. Garmin support just tells me to master-reset my watch, to reconnect to the app. All things that I've already tried.

Any ideas? I'm in strong need of the navigation feature this week for some trips into the mountains. This is an absolute bummer for me.