@ralf-muri I think this is related not just the Suunto 9, I experience similar issues occasionally with my Ambit3. However, for me the high HR value from begining of the activity is indicating bad contact (didn’t wet enough the strap) or bad battery. As for dash instead of HR value, that could be bluetooth connection issue and many thing can cause it: clothing material, sweat or again low battery level. Sometimes pairing the sensor again with the watch helps, at least in my experience.
Hope one day Suunto app will be able to display battery level of the HR sensor.