fenix 5 series: HR failures

Hi, I am struggling with a incomprehensible and not replicable error that occours througout the whole Fenix series:


HR reading failures after a certain amount of time.

This graph was done from todays morning walk.

• green line is a Polar H10 chest belt for reference.
  
• violet line is the new Fenix 5+ (got it yesterday)
  
• blue is my 2 months old Fenix 5X (has same symptoms, but not today)
  

This was a easy walk with my dog, minute 25-33 we had a break, resting on a bench, but the error started around minute 50
until the end of the walk.

The HR reading of Fenix 5+ broke down to around 55 bpm, where the correct one would have been around 100-110, as recorded
with the Polar H10 and Fenix 5X, see yourself:




This very same error already happened on 3 other Fenix watches, that I owned before since February of this year.
A Fenix 5, and two 5X's, now the same on the new 5+. I really hoped that this annoying bug is fixed on the new 5+ series.
But NO, it obviously is not.

These wrong readings happened on all Fenix watches I owned. I replaced them all within 30 days, but every replacement
showed the same symtoms after some time.

I tried many things:

• cleaning the watch in water before and after every session
  
• wearing it on the other arm
  
• wearing it upside down
  
• resetting it
  

Nothing helped. The error happens again and again. But not replicable. Sometimes the watch gives correct HR readings, most times
it doesn't.

And we are not talking about a 10% inaccuracy, that would be tolerable, but about 50+%.

I have contacted Garmin Germany support a few times already. They say they are not aware of this problem and nobody else
reported this to them. One of the support staff members said the device is faulty and needs to be replaced. I did this then, but
the error reappared on the replacement as well.
So Garmin was not of any help for now.

I was thinking that maybe it has to do with some static load on my skin, depending on what I wear, but also this is not
reproducable. Maybe with high humidity (I am at sea lvl, with very high humidity most of the time). But even cleaning it
when the HR reading is so low doesn't change a thing.

so my questions are:

• has anybody of you run into this failures of the HR sensor?
  
• how can I track this down, so that it becomes reproducable?
  
• why isn't Garmin interested to get this fixed?
  
• why is it only me that notice this?
  

These watches are expensive and top notch, but with a HR sensor that gives wrong readings on near every walk/hike
really really is not acceptable. All the statistics are wrong,
I understand perfectly that a arm worn HR sensor on a watch is never as accurate as chest worn one, but still it should
work nicely within a certain range of tolerance. Not in my case and experience with 4 different Fenix 5 models.

What are your suggestions?