recently I've got a fit file corruption while was trying to save the ride. the whole issue looks completely the same as I had a copule of month ago with 840 headunit.
after I selected the amount of calories and water, selected self evaluation 1050 just rebooted.
on the start it showed me the unsaved ride but with suggestion of 0.0 water and calories.
the fit file in the end wasn't able to synchronize with Connect, and manual upload returned an error.
Fix that @seilogramp suggests in any other thread does the work, but still I'd better see the issue fixed in the first place 
I wonder what causes the issue? is that something with self-evaluation feature? is it with calories multiplier? on the fixed FIT I see unrealistic amount of calories burnt during the ride 7000 for 120km easy ride.