Apple Watch keeps pausing during workout

My Apple Watch started behaving strangely one week ago. For two years it never had a problem. Now it keeps pausing during workouts. Oftentimes it starts pausing after 4' 47" .... occasionally it stops every 10-11 seconds over and over.... (like 10-15 times in a row). No tatoos, nothing touches the crown (I am sure about it), auto-pause off, detection of the end of the work-out is off, the watch is neither tight nor loose (same position as in the previous 2 years). Anybody has a suggestion?

[Re-Titled by Moderator]