It’s actually 25, there was a typo in the article that they fixed.

Looks like pretty classic underextrusion. Have you measured the filament diameter to see if it’s exactly 1.75mm? Even 0.1mm is enough to start causing problems. It’s prusament so should be good but worth looking! I can see underextrusion problems in more than just the problematic pillar, so worth playing with retraction and perhaps increasing temperature.

Meshmixer is good for exactly that but it’s been a long time since I’ve used the software.