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!
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.