It's utterly bizarre. I was impacted by that outage a year or so ago and they claimed that they were going provide offline syncing in the future but I still don't see it. It seems the flow is Watch ->(Bluetooth)-> Phone ->(LTE/WiFi) -> Garmin Cloud ->(LTE/WiFi) Phone. There's no reason for the Cloud step other than that Garmin wants your data but the sync won't work without it.