<p>Are these vertical lines described as "banding"?</p>

<p>Would the most likely culprit be the extruder?</p>

<p>FWIW, this was printed in "vase mode".</p>

<p><a href="https://i.stack.imgur.com/0ZCPF.jpg" rel="noreferrer" title="&quot;Vase mode, PLA"><img src="https://i.stack.imgur.com/0ZCPF.jpg" alt="Vase mode, PLA" title="&quot;Vase mode, PLA"></a></p>

Banding usually refers to Z banding and manifests itself in a wavy/non-straight wall in Z direction:
This sort of banding is related to mechanical or design issues of the printer (lead screw (nuts), belts, play, etc.)
Your print, however, shows local thicker walls. It appears that these local thicker parts are related to the change in direction of the print head. A 3D printer does not print curved lines or arcs (although
G-codes do exist for arc movement
), all movements are straight lines. So the cylinder consists of straight lines. By rendering the cylinder with more triangels you could increase the amount of straight lines to form a better approximation of the cylinder circumference. You could also try to lower the printing speed, but since you did not post any printing parameters that will be a guess.