Heart rate drops during running

You might want to take a look at this: https://forums.garmin.com/outdoor-recreation/outdoor-recreation/f/fenix-7-series/306474/has-9-33-9-36-ruined-heart-rate-monitoring

Very small chance that the new software is the problem, its very few people that complains about 9.36 - acutally i feel the heart rate sensor is picking up changes faster. Could be many things.. A more realistic guess; Are you running outdoors, and have cold hands? People tend to get weaker readings in fall/winter because of the lower temperatures = reduced bloodflow to the hands and wrist. Are you cleaning your watch? Are you wearing it as you should? Sweat? 

Well, as I said multiple times before, all that changed was the software. I didn't change anything about the way I am wearing/using the watch. It's also very slow to react when I'm not even working out. - Takes at least 20s to react to me going from rest to walking around. And I see similar things to what OP is reporting even with chest strap. Before the update to 9.33 it was all good. Ever since then the watch's HR reading give's me multiple WTF moments during my runs because it doesn't make sense.

Just because it's 'very few people' doesn't mean it exists for those people.

My new Fenix 7x has been having this issue really badly. I was running up hills on the trail and then checking at the top, out of breath and feeling like death, and it was saying my heart rate was 83. No it sure as hell isn’t! Very annoying that it’s jipping me out of anaerobic time for my training effect. It feels insulting on some level:p I did find that pause ing the activity for a second or two before resuming seems to help (sort of) but it’s very annoying. 

Wrist. So I know it’s a little less accurate, but it hasn’t done this in the past. Just started having this issue about 2 weeks ago. Also I’m not convinced the chest strap would make a difference from some of the other posts I’ve seen. 

I had something like this on a treadmill today. Did a 3 weight room workout using my F7XSS workout activity. Stopped the activity and saved it. Then started a treadmill activity.  Ran a 1/2 mile sprint in 3 minutes. It said my average heart rate was 118 with a max of 123. I know it was MUCH higher than that! 

With WHR, there is always a risk of misreading, no doubt. That said it looks like there is some investigation going on. Check out this thread and add yourself to the case

forums.garmin.com/.../hr-concerns---it-is-inconsistent

Also have this issue with my fenix 7s, on my bike ride, I do constant speed on flat terrain, but heart rate jumps from 140 to 90 for a few minutes than back to 140, any solutions? Garmin support says like they monitor is state of the art and it's perfect which is not kind of helping 

I have this same issue!!! It floats between 80-90 while RUNNING running and if I cross check with my treadmill my HR is in the normal range of 140-160...this has become some worrisome that I am thinking of demanding a new device from Garmin. Pretty *** stupid that a $1500 smart watch cant even do a BASIC function like read HR properly.