The Watch restart and activity is missing.
I've had similar situations before. When I was running, while checking my running pace, I noticed that the clock was resetting, but it went back to recording activity. At the end of the run I was able to save the activity. The only trace after the reset is that in my activity I have an unimaginable increase (peak) in running power from several hundred watts to over a thousand.This time the activity was lost and not saved.