As shown in the above screenshots, my HRM works fine for the first hour or so, but seems to either suddenly or gradually drop down to about 60bpm and didn't usually pick back up. I'm using the original Garmin HRM Dual strap with the sensor, about 3 years old, and it's connecting to the Edge 520.
I have replaced the battery, washed the strap, reposition the strap on me when it drops off to try and get it to 'reconnect' to me, but my HR definitely doesn't drop off as I was wearing my watch at the same time giving me a consistent HR.
I'd assume something was wanting replacing, but as it works fine for the first hour or so I can't really work out what the issue is.
Anyone encountered anything similar or have any suggestions?
Thanks