Android Garmin Connect sync service disappears

Hi! 

I used to have a constant Garmin Connect sync service running on my Android phone (a constant notification showing it was running). Recently  (past week) it seems to have disappeared,  and the Connect IQ apps on my watch (Venu) also seem to be experiencing connection issues, and I'm pretty sure there's a relation.

After rebooting the phone, the sync service notification returned,  but disappeared again after a few hours. The "Connect" app has "Unrestricted" battery permissions (Samsung phone), and it hasn't changed since I first installed it a few months ago. 

What could have changed that is causing the service to be (apparently) killed off?

Thanks for any clues.