Experiencing this on watchOS 5 beta 1 and watchOS 5 beta 2 with a Series 3 cellular. The watch will randomly restart. This seems to happen 5-10 times a day.
In addition to restarting, the watch sometimes appear to get "stuck" between locked and unlocked. It appears locked (calendar complication says "unlock to view" and activity rings are greyed out), but when I tap the face to put in the passcode the watch is actually unlocked (a tap on the calendar complication takes me straight to the calendar app as if the watch is unlocked, a tap on the activity coimplication takes me straight to the activity app).
I just installed the sysdiagnose profile and will be submitting my logs to Apple, but was curious if anyone else has had this issue and found any solutions since my watch is mostly useless as a result. I have unpaired/repaired and set up as a new watch, which helped for a little while and then the same behavior started to happen again.