Any time my iphone reboots, my garmin connect acts as if my fenix 5x is new (but reconnects) and my edge 830 is missing. The Bluetooth pairing is there, so this is NOT an iOS issue, but one in the application or edge 830.
After deleting the edge 830 items in bluetooth, then forgetting the pairing on the device, I can reconnect it again after. After the configuration goes through, the device will attempt to sync where it will 100% of the time fail. Quit the GC app, start it again, and it may sync properly.
Will work "fine" from that point on until my iphone is rebooted again, where the same process occurs. This is a 100% repeatable situation.