[Closed] anyone else have their hrm stop working at the same point each time?

I've had hrms for along time now but in the last few years I've found it starting to stop working if I push it very hard. I've previously blamed it on the hrm i was using (Garmin with hard strap) but lately I've tried it with 2 others and they both also stop working at the same heart rate each time so the problem is likely me

I'd be more worried if I hadn't had a full heart check up a couple of months ago including an ultrasound and test on a stationary bike and was given a clean bill of health. Of course they don't really test you at the sorts of levels you get pushing up a hill 🙁

Has anyone here ever had something similar or have any idea what sort of place you would go to get it checked?