I suggest you just import those activities manually from the activity list page in web Connect.
This issue seems to be resolved
REKsRun Former Member
Have a look at the answer posted by Xraydog
Also this post might help resolve your syncing issues: Sync / Connection Troubleshooting Guide
Connect your device to a computer using a USB cable.
Open the files associated with the device. Under "Activities", you should see the activity appear as a file with the date and time of the activity that failed to sync.
Login to web Garmin Connect. Go to activities page. Select "Import".
From there you should be able to drag and drop the file to upload it.
This should work so long as your device recognizes it as an activity.