Heart rate inaccuracies

According to my experience with wrist heart rate sensors, they struggle with sudden changes in intensity. For long steady runs, the wrist heart rate is fairly accurate in my case. It is usually okay for intervals as well, particularly if I ramp up the speed instead of going directly to sprint. If I try to beat a short Strava running segment, sometimes the indicated wrist heart rate does not go up at all until some time after I was finished. For these runs, you need a chest strap to get reliable data.

Thanks ovekvam, back in May it seemed to working fine with my max heart being reached during races peaking at around 207 bpm, but now it seems to only reach 145 - 165 bpm.

Which SW have you had in May? Till 16.xx it was fine IMHO, after the update is now very unstable, sometimes I am getting 150 on recovery runs (should be max.110). Sometimes it does not react at all to HR changes. 

Now we have a watch w/o instant pace and very unstable HR counts, but hey, it displays my pace from stryd and HR from chest stripe.  

I'm not sure which software the watch had when I bought it. But my training load was showing a strong upward trend (and it should still be) but ever since the update it is continuously dropping and going back into 'peaking' because it is not registering any of my high intensity workouts. It makes the watch almost useless (unless you have a chest strap) as a training aid when it can't track accurate heart rate and/or other statistics. 

https://connect.garmin.com/modern/activity/16693660493

Here is a run from today where I didn't have my chest strap available. The wrist heart rate was not keeping up at all. I was running 800, 700, 600, 500, 400, 300, 200 and 100 meters. Almost every sprint jumped up to around the correct heart rate a few seconds after I went back to walking. 

The watch failed completely logging the 100m, which was 14 seconds. I got zero cadence and zero running power despite running around 2:10 minutes per km. 

For training like this, you need a chest strap.

I bought my Forerunner 255 in May as well. All was working very well in the beginning, but more and more often the heart rate seems to be wrong and too low compared to what I've had in the past and how I feel.

In the beginning the trouble only seemed to come when I was riding my bike. I kind of accepted that maybe the clock wasn't made for cold winds through my wrist when riding. But now it seems to not handle anything when I'm running either. 

Gonna complain to support on Monday. If they say this is normal I will return my watch because then it's a product not living up to what they promise.  I have the law on my side thankfully.