HR during strength training way off

Yet again I come seeking help due my Vivoactive 5s complete inability to track my activity. 

After months of issues with running, which now appear to have been fixed, I now have issues during strength training (walking was also never fixed). 

Doesn't matter the activity, my HR will ping all over the place. Going up to 110s for a second then plummeting to the 50s. Thus I'm getting virtually no active minutes from almost an hour of work. 

I've sent a ticket but had no response and I'm getting to the end of my tether with this device. Fitbit was useless so I'm feeling backed into a corner just by wanting a watch that tracks my activity - a bigger ask than it seems apparently.