I had the same problem. After reading many posts I determined it was due to moisture in the watch. Despite the specs this watch it not water proof at all and once moisture gets in it, it shorts the switches and goes into a reboot mode. You need to get the moisture out to get it working again.
My solution (don't laugh), an air fryer. Pick the lowest reheat setting you can. Mine was 170f. I had it in there for about five minutes and when I took it out it was very hot. I got a high temp warning from the watch and it shut down. When it cooled off I started it up and it acted like it would after a factory reset. No problems after that, but now I know I can't get it wet.