Hi,
I have Garmin 610.
I installed ANT Agent on new PC few weeks ago - the same problem. Workout was synched, but not shown in Garmin Connect site.
I installed Garmin Express on new PC - the same problem.
The only way to successfully send the workout is to pair the device again in ANT Agent, but it sends all the workouts and takes more than 1 hour. Pairing again in Garmin Express doesn't help.
When I tried to use my old PC with ANT Agent software installed long ago, everything works like a charm.
Can you please check the problem ?
It really made watch not convenient to use.
Rafal