I had had some under-extrusion problems that led me to replace my hotend and get a new hobbed bolt, and today I found by accident, that my filament roller bearing had some gunk inside it, that made it bind up at certain points in its rotation. This may have been the cause of the extrusion problems, if the bearing was bound up at the same point when the extruder motor was trying hard to shove a bunch of filament down the hotend, causing the hobbed bolt to slip and carve into the unmoving filament. The slipping would make less filament come out, or none, until there was less demand (less pressure in the hotend), I’m thinking.
I just rinsed out the bearing until it spun freely, dried it with hot air, and re-oiled.