Sorry to post in the 820 section but there isn't an 810 section!!
I am finding that my 810 regularly switches off mid ride. It only does this when I am following a course (never when I am simply recording a ride). I can switch it back on again and I am at the "save" or "discard" screen. I press "save" but then I have to stop and switch off and back on again and wait for GPS connection. This is frustrating for three reasons. Firstly I have to stop the ride, secondly I have recorded two rides when I did one, thirdly, I don't always spot this immediately so I have missing miles.
Anyone found a solution?