I had this exactly same problem on a Fenix 5 already before. Now after a few weeks it is the same on the 5X:
the heartrate shown is mostly wrong since a few days. Always around value 40 lower than real.
See attached 3 images, one graph is from the Fenix5X, the other one is from a Polar H10 chest belt, which is accurate.
First I thought it has something to do with the kind of clothes I am wearing. But I was not able to get it correct again after I changed to all possible clothings again.
I also factory resetted the watch and washed it carecfully in warm water.
Nothing helped.
Any idea what's wrong with my watch?
This is a graph from this morning, easy walk, the fenix was totally wrong.
ciq.forums.garmin.com/.../1344992.jpg ciq.forums.garmin.com/.../1344993.jpg
