@zagazoo for spikes problem with external HR sensor ( chest or optical band ), solved twice by re installing the app.
I got that problem one year ago, suunto race, and once again a month ago, vertical 2
As Suunto support explains to me there are different heart rate algorithm wich took place, once before start activity ( when external device is detected and read before the start, one during activity, showed on the screen, one to create the summary graph on the watch when activity ends, and also one when sync with the suunto app )
In my case the final on watch report was good, but spikes were noticable during activity ( data on screen ) and also on the app report.
Re installing the app solved the problem each time.
Strange isn’t it ?
Hope it will help