Erratic Wrist based Heart rate : BUG + Root cause

I think the latest 16.17 update has fixed this issue.
The problem before was the watch kinda not "believing how high my heartrate was" and get stuck in 8x or 9x.
But me being terrible at sports, regularly goes above 100 when walking, and 14x just after one minute of riding
After updating today, I did two bike rides, both times I didn't "pre-enter the workouts ready page to let the heartrate settle, I just press START, select Bike and start the workout. Both times it just started my heartrate at 100+, and locked onto my (maybe) true heartrate for the entire ride.

Before it refuses to believe my heartrate is 100+ before I even started exercising. Now it totally does, and I am so happy with this update (along with other nice fixes and additions)
It will take more testing to be sure, but yeah this update is looking promising!

Started the workout midway through a short bike ride, picked up heart rate after 2 minutes. It's not perfect, but a lot better. At least it doesn't refuse to believe my high heart rate when a workout started and never (or take up to 30 minutes) pick up the heart rate now. 

I noticed a difference with my first gym session on version 16.17. The reported heart rate has been rather low for my strength sessions, but was now reporting higher than usual. Seems quite correct. It also gave me a more suitable training load because of that. Thumbs up so far.

True, I feel like the new update kinda fixed this issue and not just me imagining.

Now I can actually get train load and actually useful stats for my 10 minute home to campus bike ride. 

I don't really care about my heart rate graph is flat the whole time, because let's be honest, we don't view the graphs every workout or are able to interpret something useful from the graphs and the HR value.

But the problem with training load and effect is quite a big deal, and I'm really glad that it is now fixed. I may start the workout when my hr is high without worrying it will never lock onto the actual heart rate. Before, for the workouts that matter, I have to initiate the workout and stand there, wait for the hr to lock to around 100~110 before starting the workout.

I have noticed a change for the better in the readings of my 255 after the last update. 
Without a doubt, Garmin technicians have been working on improving its operation.

Thanks for your analysis, ovekvam. I totally agree.

Fortunately, it seems the problem is solved with update 16.17. Today I have ran again with the same setup (Vivoactive 3 + band  and FR55) and same path. The pace was lower (I pushed too hard at the beginning). Still the cadence was more or less the same as the previous tests and close to my real heart rate. However, this time heart rate graphs and the average heart rates (156 vs. 157) from both watches were pretty closed. It seems Garmin has improved the filtering! ;)

I've noticed a problem with my 255 recently. Mainly it is ok but it would appear that the pointer in the zones is incorrect. Doing a parkrun on Saturday display showed HR in Z1 which is clearly wrong as most parkruns are in Z4. After a steep incline it suddenly went to the red zone! When I uploaded my run it would appear the heart rate data is correct despite what was showing on the watch screen Could this be right? one way I have found this to get working properly is to lift the watch off my wrist for a minute or two and everything then seems to report accurately on the display. Very odd. Just wondering of others have spotted this.

Yes

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France

This morning, everything was working fine until 30min. Past that, the HR suddenly dropped below 100bpm which is impossible as I was doing 6' runs at 4:36/km. At the end of the run, when running slow, seems like it was back to normal.

Any way to fix this?

Same here today. HR missing for a while, then showed again but droped to much lower values than my real HR. I'd HR between 160 .. 180 during this session, definitely not below 100.

Forerunner 255 (not S/music), FW 17.26.

Also experiencing issues on Forerunner 255S Music FW 17.26. HR seems to just drop or increase randomly by a fixed amount. For example my HR could be stable around 150 then suddenly becoming stable around 170. Then later coming back to being stable around 150. In that example it seems to be just an offset of 20 added to the HR for no reason. Is it possible to get an update on this or should i return my watch ?