Hi,
with the most recent Garmin Connect release, there appears to be an issue with the export function (to GPX/TCX/KML) for certain activities.
See these forum threads for more details and activities that reproduce the problems:
https://forums.garmin.com/showthread.php?170557-Route-export-(TCX-GPX)-failing-this-morning
https://forums.garmin.com/showthread.php?173323-Did-the-14-10-release-of-Garmin-Connect-API-break-TCX-exporting-in-some-cases
It would be great to see this issue resolved.
Thanks, Peter