I’ve been suspecting this happening for a few weeks, but finally caught it in the act. I was taking a shower this morning and glanced down at my Apple Watch (Series 7 cellular)… 8:46.  8:46?!?  I didn’t think I had been in the shower that long. Brought my wrist up, and the time changed to the (correct) 8:39.  Happened again a few minutes later.