It’s definitely being under extruded. As to what’s causing that, my first guess would have been a clogged nozzle… but if it’s happening not-at-random, it’s probably not that.

is there a way to see a log of hot end temps across the prior prints? it could be that something is causing the the machine to speed up putting out more plastic and the hot end struggling to keep up, though I’m just spitballing here.