Recent Crazy Maximum Heart Rates

Hi, 

Since the 1st August I've had a number of crazy maximum heart rate readings.

  • My max heart rate is around 186, but on 7 occasions since the 1st August my heart rate has gone way above this, sometimes going as high as 222, but not during any of my sessions. 

The latest reading was on Sunday just gone. I attach a screenshot of the day. I went out for an easy run in the evening during which my heart rate didn't go above 150.

The rest of the day there's been no spikes so I'm really confused why it's registering as 218 on this day.

Definitely didn't go high during the run as I watch it like a hawk, and during the day no stress and no high readings registered on the graph. 

I have a Forerunner 965 and use the Garmin Hrm-Pro strap during the runs. 

Assuming this is a software issue... Any ideas?