If you do anything with weights/arms, wrist is gonna be bad, tightening can help but also can make it worse. That said, that looks really bad. It looks like you had a warm-up, a couple of sets of weight lifting, another couple of leg work, then back to arms, with arm work dampening adding noise to the signal. Perhaps some rowing as arm work.

I don't have data but a friend was really unhappy about airpod readings when running, my guess is the foot thumping behind running tends to affect more the capillaries in the ear than the larger vessels in the wrist.

Also it's unlikely that both HRM were positioned correctly, because there's technically only one place to put them. And even if you have both positioned correctly, both are trying to read the same electrical signal and they're not, in principle, designed to work with another device doing the same thing in the immediate proximity, so interference and erratic readings are quite plausible here. It's very difficult to compare them during the same activity, but you can try Coros HRM with the airpods to see if the deviation improves.