I recently needed to delete the GCM app because of the amount of problems I have had with it, though I question how many are because of the app and how many are because GC is moving forward and Garmin isn't keeping GCM in sync any more.
I have attempted for two days now to connect my device back to the app. It pairs via Bluetooth without issue, but then gets stuck with a "Connecting" status and the little man never stops running. I have given it hours. I have uninstalled and reinstalled the app again. I have rebooted my device numerous times. The most frustrating is to even get this far I need to delete the pairing out of my Bluetooth settings each time I try.
It has already been weeks since the app actually synced my data other than showing real-time stats and giving me access to the devices smart features. Asside from that all syncing has needed to occur using Garmin Express. This really needs to be fixed or I need a full refund for my Garmin device (Vivoactive3) and all my accessories (Footpod, Speed sensor, and Cadence sensor), because right now I can't use the device the way it is advertised or intended.