Wrong heart rate monitor during training

Wrist HR is never going to be perfect. Doesn’t matter if it’s a $1000 watch or a $100 watch. Just use I it to  track your general trends . Even the chest heart rate monitors struggle with accuracy

Thank you for your answer and your time.
I am aware of the problems regarding measurement accuracy (especially with optical pulse sensors). But how can it be that it deviates by >40 beats and then temporarily displays correctly again? I must honestly say that I am becoming very disappointed with Garmin.

Depending on your how your body is built, you can get this with all optical sensors, or only with some, or none. No sensor is fit for all. For some the old sensors are better, for some the new sensors are good. For some none of them are accurate. That doesn't depend on the price of the device. It depends on sensor technology and how it is matching your body. 

Marcel said:

But how can it be that it deviates by >40 beats and then temporarily displays correctly again

Watches move during exercise particularly due to loosening, sweat, heat etc. I often have to tighten the watch an additional notch or two during a run. The problems seem to be exacerbated when running on hills and trails. Basically, it's something that can happen with OHR. As noted the cost of the watch is immaterial; OHR works better for some than others. For those reasons, a strap is strongly recommended for people who are really interested in using the performance metrics of any watch with OHR.

You should still talk to support in case there really is something wrong with your sensor. It might've gone into low power mode for some reason. We can't tell, of course. 

I had similar problemnwith my Garmin Epix i.e. incorrect high heart rate measurement during couple of minutes in the beginning of a run. Garmin gave me a new watch but this Epix has exactly the same problem again.

Like you said it makes al other analytics useless. Very disappointed about it.

I had 3 other Garmin watches before, all much less advanced and cheaper and never ever had such an issue with those watches. 

Edwin

I am currently having this same issue. It seems to only happen when an activity is underway. I recently did a 10 mile walk and for about a 15 minute timeframe my HR registered at 61bpm when my average for the walk was 136pbm. I rarely even hit 61bpm in a resting state. It occurred again today which is what caused me to go searching for this thread. I was on a casual walk with my kids where my average HR was 114, however it showed 68bpm during the activity. I then closed the activity and it immediately shot up to 98bpm. I understand these aren’t perfect but that’s no excuse for something that are clearly complete errors.

I have the same issue while walking. Stop and start the HR sensor seems to temporarily solve the issue.
I have the feeling that it worked fine fine when I used my epix at the beginning.

I have the same issue with my Epix 2.

Way off (50 under) on treadmills every now and again.

It does this for 20-25 minutes at a time and doesn't correct itself - 115hr shown vs 170 (real hr measured on the machine)

I don't remember having this issue last year when I got the watch at all but it's been happening a lot in the past month or two.
I wear the watch snug, sensor is clean, on the latest software and even joined the beta (11.28) but it still happens.

Really hoping they fix this as it seems to be an issue that started happening with recent firmware.