I posted this in the 935 forum, but I thought I would reference it here too in case it is limited to the iOS Garmin Connect Mobile.
https://forums.garmin.com/forum/into-sports/running/forerunner-935-aa/1437017-workouts-calendar-not-sending-to-935-gcm-iphone
I can sync through the website and Garmin Express, but not using the Garmin Connect Mobile app.