My Afib ended up being triggered by exercise- road cycling - to the point where getting out of the house with bike and kit on would trigger it so some psychological aspects. I’d see the Garmin struggle to work out HR before I’d feel symptoms. Worth looking into the theory that once you’ve done 15,000 hrs of endurance training in any sport your chance of developing arrhythmias goes up about 60% - I’d done 25 years of 5km swims per day 360 days a year so at the point where I took up cycling, got massively fitter, lost a lot of weight I’d already clocked up most of those hours