I have Afib and it shows up every now and then like what you've described. But, yours could also be a faulty strap. Does Jim have a Garmin that you could also wear at the same time with his Computer just to see if it shows up on both.....assuming you can eliminate any cross talking between the two.
Good to hear you're still riding. Would love to get back to The Springs again!!
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Ride your Ride!!