I've seen that quite a few people have had problems with Connect and/or Express over the weekend. I'm in a similar position.
Tried to sync my Forerunner 910XT yesterday (Sunday), and Express said the data had synced. However, Connect wouldn't recognise any of the workouts I'd done last week.
After reading that other people were having the same problem, I gave in and tried again today. After re-syncing, today's run has appeared in Connect, but none of last weeks workouts. While they are still on my 910XT, the files have not appeared on my Mac despite Express saying that the data has synced.
Any suggestions welcome!