I have been having the same problem with my 910xt for the last week.
I go to upload my data and the Garmin Express screen shows that I have 150 items to sync, 3+ hours remaining, and all of the activities are either from July 5 at 12:33pm (17 activities), July 5 at 12:34pm (18 activities), July 5 at 12:35pm, etc., all the way to July 9. The watch shows that it is transferring data, but there is very little progress being made on the transfer and eventually it times out.
Here is a picture of the screen I'm seeing:
I definitely don't have that many activities to transfer. Maybe 3 or 4. Usually it syncs in a matter of seconds.
I have tried uninstalling and reinstalling the ANT+ drivers and Garmin Express.
Can someone explain what is going on or how to fix this transfer problem?
Thanks,
Mary