I've just bought the forerunner 920xt. Under deivice settings the auto upload option on my app is locked. My phone is syncing with the watch, but will not upload any workout or steps data.
The AutoUpload switch in Device settings is set to always on and you can't change it. It looks as if it is off, but it is on. If nothing uploads, there may be a corrupt file on the 920xt. Make a backup of the /Garmin/Activity and /Garmin/Monitor folders, with device connected to computer via USB. Then remove the files in those folders on the 920. Record an activity and sync again. If that still doesn't work report back here.