I’m having the same issue. Wouldn’t it be great if Garmin could admit to the fact that there’s a bug and tell us they’re working on it rather than just sending us to Garmin Express? BTW, GE didn’t solve anyone’s problem.
My S20 has worked reliably until this Wednesday after which it syncs ok to my iPhone except my golf stats are missing. Steps etc are recorded (not interested in them but it shows the devices are talking ok) but no golf and nothing is being uploaded to Garmin Golf. When going into the Connect app setting and clicking on Garmin devices I see an exclamation mark next to the S20 and it states ‘Sync failed-server error’. I’ve deleted and added the device again just to remove any issues there but the error persists.
Looks like not just limited to S20, my vivoactive 3 is exhibiting the same issues. Appears to save the round then only the activity appears on Connect, no scorecard to GGolf...all rounds since UK lockdown allowed not saved, frustrating...seems every update to fix one bug, creates another...