I have a Nike Edition series 2 running WatchOS 5.1.3 (16S535). Every so often it will started rebooting and even a hard reset doesn't stop it. In order to fix it I have to keep reloading from previous backup from 12/4/18 (Which is a clean new watch install on 5.1.1) Since upgrading to WatchOS 5.1.x I have been experiencing this weird issue. My son has the same series 2 as I do and his doesn't do it. I have taken all the apps off except for the 5 or 6 that I have used since getting my Apple Watch. Anyone else experience this issue?