HR accuracy issues

Is there anyone else having issues with HR readings?
I noticed that my HR was "stuck" during workouts, and would never get any higher than ~100.

I've tried wearing the watch in maybe 10 different ways, other arm, removed all sweat, tightened the strap, etc.. nothing worked.
All software is up to date.

I had a friend nearby who has a FR 235 and that watch reported HR 142 while mine was displaying 101. I think that's different enough to say that it's not working.
It sometimes work , and sometimes not. Can't make head nor tails of it...