Awesome thanks Rob! I think the problem is running. 
it picks up cadence, would be happy to be proven wrong, so maybe test running as well. Little side project for you! Appreciate your help!
MJ
Hi Marjaana, the screen shot is frm my mobile. Never mind - we’ll see what happens the next time I do an indoor bike workout.
Hi Robert, thanks for all your efforts! I would like to try my Polar Verity armband and see if I can get it to override the Garmin HR - except the battery charger seems to have disappeared 
If it doesn’t show up maybe I’ll invest in a chest strap.