I got the same problem with SOME data failed to transfer thru GCM such as activities.
My local Garmin support recommended me to reset and reinstall everything. Do not repeat this mistake as you will lose ANY bluetooth connection.
12.2 beta 1 does not let you add your device to GCM. Roll back to 12.1.3 non beta doesn't help as well – do not waist you time (as I did).
You'd rather wait for a more stable iOS release and use cable connection via Garmin Express desktop application instead.
Oh, so it's a beta iOS issue? I'm so relieved :) I've been doing the whole dance of deleting everything from the watch, thinking something was corrupted. In the end I even restored it to the factory settings.
It was weird because express sync works normally, and also if I force quit the app, the 935 can sync via wifi.
Well I guess we just wait for the next iOS/GCM update and till then wifi sync it is.