Garmin Connect app won't even show you data sync'd from a watch unless its online and connected. Simple things like hours slept, or miles walked will not show. Right now it just has a "server maintenance" message, and won't show anything that uses a graph, or historical data...nothing is stored locally.

On my recent hiking trip, the watch had no problem recording and sync'ing tracks, but the connect app refused to render any of that data until mobile data was connected again.