I recently updated the firmware in my Edge 810 to 3.40. I did a full factory reset, and then 2 rides. Neither will upload manually to Garmin Connect - I get an 'invalid format' (if I remember correctly) error each time I try. I have no choice but to manually upload them, as Garmin Express refuses to run on my computer - and I'm done messing about with it.
Of course, both rides upload without problem to other online services such as Strava, Ride With GPS, Endomondo - as well as various PC applications (Golden Cheetah, Power Agent). Only Garmin cannot read data collected by a device of its own creation..... :( Go figure.... :(
Maybe one day they'll hire a REAL programmer......