Is there any way to encourage Garmin to prioritize the bug fix?

If you look under the back of the watch when your app is running, are the leds flashing or on solid?

Flashing is 24/7 mode and less accurate.  make sure you enable SENSOR_HEARTRATE and the lets should be on solid.

Well in most of the cases it is solid but sometimes when I open the app (not yet recording activity) it is flashing - if so it keeps flashing even when activity starts. I guess when 24/7 mode is on the HR chart is stepped (I did describe it here: https://forums.garmin.com/developer/connect-iq/i/bug-reports/bug-hr-data-issue-low-value-and-sampling-rate-for-custom-made-apps). I will review my code again for enabling the sensor.

Unless you properly enable SENSOR_HEARTRATE. you also won't get data from an extremal HR sensor

If you properly connect to an external sensor and it's transmitting, you can take the watch off and still see HR data.

Well I tried enabling/disabling SENSOR_HEARTRATE and the behavior is the same - low HR reading during activity. 

as in orignal post I'm looking for some advices how to make garmin prioritize bug fix

How do you know the HR you see is low?  Is it just not as high as you expect?

Do you see the same with an external HRM?

I can see your point and I normally I ask the same to the users as many times their perception is based on the 'feeling'... 

1. these problems started suddenly after one of the updates released by garmin therefore every single user saw significant drop in HR from one training to another - eg. in my case until the bug EVERY tennis session was at 170-180bpm which was reasonable since after a lot of rallies I could not catch a breath. Then after the bug was introduced by one of the update the average hr droped to 100bpm and it is at this level ever since but I'm still paying at the same pace.

2. Every single user tells me ( and I can confirm from my experience) that if default tennis app is used the HR is at the level before the bug was introduced.

3. When I look at the HR rate during my sessions it just stays the same or at the similiar level. Here is an example:

For some reason session started at >95bpm level (my resting hr is somewhere around 60bpm) but then session started after 60sec and I was looking at the hr displayed by watch which was not going up so after couple of minutes I did pushed myself harder, felt my hr going up and as you can see the reading even went below the average line.

Then I got pissed off so I restarted the session and here is HR for subsequet 38mins:

Then I also saved another 10mins with app version without enabled SENSOR_HEARTRATE explicitly -no change.

Here is a HR from default tennis app which I recorded recently:

I'm not an expert and maybe 100bpm is more accurate (doubt it) but if so why default tennis app shows 170-180?...

Anyways right now this issue shows up on more and more garmin devices and as you can imagine this ruins the training readiness, body battery, calories burn etc.

Do you have another way of recording HR? Like an old watch? Can you try to record the HR with another watch using any built-in activity (which according to what you wrote would give the correct, 180-ish HR) and put below it what your app records at the same time?

If this is happening, understand it's more than likely not CIQ but a firmware issue.  Has this been reported in the device specific forums?

Yes, i have few garmin models but what would be the point if there is no way of getting these issues fixed.. And I kind of understand garmin devs have no time to address it but on the other hand this particular issue 'spreads' and more and more devices are impacted. Initially i taught it is just a bug as even someone from garmin did contact me about it and in fenix7 it was gone for some time, then I taught it is intentional to discourage people from using old devices (similar to lack of support for activity types like squash) but it also happens on newer models. Now I think maybe they just dont want people to use ciq apps...

I try to report bugs, some are unique to particular models which I know will never be fixed (like fr55 accelerometer bug) but I report it to demonstrate to my users that at least I try to get it fixed. Eventually I rollback support for those devices at some point in order not to deal with unhappy users (eg. Fr55 accel issue makes my apps useless so noone impacted by this bug will ever use it anyways). 

I'm afraid half a year from now all garmin devices will give fake HR for ciq apps and in order not to explain it every day to few users I will just give up on app dev and continous support and i will become (2 out of 5) 'good idea but gives poor data. Developer unresponsive' dev. Assuming the bug is not intentional I wish there was a way to escalate it - most likely there are more urgent bugs that garmin should address (like random restarts while recoring activities on Fenix7 ) and would love to hear there is a way for us to excalate - eg. there is a voting system for each bug - if I make 1000 users to upvote HR issue will it be prioritized or not? If not will 10 000 be enough or it is a dead feature..

It was reported twice as a bug and more than once (once by myself) to Fenix7 forum. Now more devices are impacted but I will not create new threads about it anymore. 

On one of the bug reports where I describe low hr and stairstep look of the HR chart there is a response from Richard from garmin that he sees it as well and thats all.