As for the syncing and re connection problem you are experiencing, we are researching this to determine the cause. I apologize for any inconvenience this may have caused.
Try this, it worked for me today.
GC app --> Garmin Devices --> select Edge 820 remove device --> restart phone & 820 --> readd 820 in GC app.
Restarted my Edge 820, 3 times this am and it connected via BT each time.
Haven't use on ride yet.
GC ver 4.16.1
Android ver 9