did a run today with my forerunner 955 (update version 18.22 from today):
first km slow: pace 6:04 min/km, av. heart rate 151
then 5 km fast with pace 4:51 min/km; av. heart rate 133 ?? (my common hear rate at that pace should be 180-190)
a sudden drop of the heart rate appeared approximately at the change of pace
All,
If you have not yet contacted Product Support directly, please 'vote UP' on this reply if you will allow me to add you to our internal report. I want to make sure everyone is added to the impact of…
All,
Thank you very much for your feedback so far on the Optical Heart Rate performance. In addition to what is already mentioned in The Heart Rate Sensor on My Garmin Watch Is Not Accurate, I want to add…
All,
Thank you for providing your feedback and activity examples. We appreciate your engagement and are continually improving our products based on customer feedback. If you can, please continue providing…
All,
Thank you very much for the examples you've provided here so far. I'm very sorry that the update did not resolve most of your OHR concerns. In order to look into your individual activities…
I would like to know why Garmin, instead of continuing to offer us copy and paste advice with which it clings to straws, does not fix a recurring problem throughout the forum, if the frequency worked on…
1. release watches that work absolutely solid and deliver useful measurement results.
2. render them useless by developing buggy firmware with more and more gimmicks and accumulating bugs. Ignore your own…
I have also the same problems. Yesterday, I went running with 2 watches, my former VENU on the right wrist and my new 265 (sw 18.23) on my left wrist.
265 : Average / Maximum HR : 143/151 
Venu : Average / Maximum HR : 168/180. Which are objectively the right figures
So big errors can be dangerous!
I have had similar issue with optical heart rate. I have had long runs when the heart rate drops to 80s and it picks up 20 minutes later at 160 (before the update in 40F temperature). Also some runs I can tell I am pushing but my heart rate is below my base runs (after update) specially towards the end of the runs. see below for the example of each one.
The bad thing is that lately you can't even rely on a chest strap.
