I wanted to see if anyone else was coming across this before I report it up to Garmin.
Immediately after lengthier, more strenuous activities (say when my bpm stays above 150-160 for an extended period of 45 minutes or more), the watch seems to stay "stuck" at an elevated heart rate. It usually fixes somewhere between 130 and 160. I can manually take my pulse or take it through a blood pressure machine and can confirm that it's actually closer to 80 or 90. This seems to stay "stuck" for quite a period of time - I've seen it go for 20 minutes or more. However, if I restart the watch, the HR will drop back to the accurate reading of 80 to 90 post workout. This doesn't happen with shorter workouts. And yes, I have checked to make sure it's actually not just my heart staying elevated. The watch even shows there's an error because if I re-start it immediately picks up at the right pulse rate.
The OHR seems to be working fine otherwise (I mean as fine as OHR can work). I hadn't noticed this until more recently, so maybe something with the firmware? Although I hadn't really watched it that close until recently. I'm just worried that this will affect other metrics including HR recovery, calories, etc.
I have a Garmin HRM that I will try next to see what happens when I switch off of that post activity.