Garmin Express started producing errors while trying to sync workouts recorded on my Concept2 rower using Forerunner 610, that's after months of seamless operation. It still syncs other (outdoor) workouts just fine. The asnwer from Garmin Support was as follows:
"As the data you are trying to upload is from a third party unit, I'm afraid we are unable to offer any troubleshooting as to why this may not be working."
I found non-uploaded temp files in the Devices folder according to https://support.garmin.com/support/searchSupport/case.faces?caseId=%7Bb2320530-05f0-11e4-eaba-000000000000%7D, added .fit extension and uploaded to Endomondo (uploading to Garmin Connect won't work, there is an "undefined" error popping up during the import session). Endomondo shows workouts with all data as usual, so this may probably be a Garmin Express / Connect issue.
Will try removing the current Garmin Express and installing some legacy version, see if this works. Otherwise any ideas what could go wrong?
Oleksiy