Enduro 2 and HRM Pro Plus issues

Not sure if this is the right forum. But cant find anything else to use.

Hello, everyone,

I have recently suspected that my HRM pro plus has not been reading correctly.

Yesterday this was confirmed to that extent.

I attempted a threshold test and ended up beating my 1km PR by 16 seconds and my 1 mile PR by 21 seconds. Despite this, during the hardest part of the test I didn't get above 158bpm. When I paused (because I simply needed a break) and started the clock again, my heart rate suddenly shot up to 175bpm.

I've attached a picture where I've marked the time I ran the fastest.

(The blue is pace and the gray is heart rate)

I'm now using my Polar H10 heart rate belt. But would you file a claim with Garmin or wherever you bought it?

The belt is just under 1 year old. And here in Denmark you have a 2 year warranty.

Image of HRM