I have an Edge 500 (software version 3.3.0) & Garmin Express 3.1.8.0.
Until a couple of days ago activities always uploaded without any problem to Garmin Connect. No activities from the last few days will successfully upload despite multiple attempts over several days. I have checked your FAQ and can confirm that the Garmin Core Update Service is running. I have tired manual uploading and uploading via the Communicator Plug-in buts these also don't work although they too have always worked in the past.
The Express error is "There was a problem communicating with the Garmin servers. Please try again later."
I can upload these same activities to Strava without any problem!!
It seems I'm not the only one having this problem but I haven't been able to find a solution.
Please tell me how to fix this.