Hi
For a number of weeks I was very frustrated trying to sync a Forerunner 305 and a Forerunner 920xt to Garmin Connect, via Garmin Express.
After countless hours surfing all kinds of forums and trying every possible solution that had worked for someone else, with no success, I accidentally found the problem preventing the computer to recognize the watch, and also the watch to sync via Garmin Express:
Both, watch and computer, have to have the same date AND time. I discovered the solution while traveling: the minute I had the same time and date on computer and watch, the problem disappeared, like magic.
Not sure if this makes any sense, but decided to post it in case it helps someone else.
Happy training