Occasional high HR readings?

Hello,

I've a Fenix 5+ and overall I'm quite happy about it, but there's one thing what's irritating me and that's an occasionally misread of HR.
I've attached two examples and you can clearly see a sudden increase of heart rate while pace remains constant. I'm running with a cadence ~180 steps per minute so I don't think this is a cadence lock (since the spikes stay well below the 180 bpm), but I'm not entirely sure. I do wear the watch quite snugged (about 1 cm above my wrist bone) during an exercise. Does anyone experience similar issues and know what's causing this issue?

Best regards,
Leon ciq.forums.garmin.com/.../1467835.png ciq.forums.garmin.com/.../1467836.png