I have the same issue. What is the solution?
Update: my graphs are back! Checked between now and an hour ago, they’re back all of a sudden!
I had the problem at this morning just for few hours but after syncing the watch again it seems the HR is back again. Im on Fenix 6x pro / iphone x .
The problem is still appearing. I have a Forerunner 935 and an android phone. Heart rate history (day and longer) is missing in GC; the 4hr graph is available on the watch. The data is also missing on the GC website. Sleep state have been missing since two weeks as well.
The same for me: Fenix 3hr and the FC records and daily steps are gone from the app and webpage. In my watch is all ok. I think is an app problem, iOS 14.6 update or anything else.