Normally you’d post a FixMyPrint issue where the OP asks for a solution. Here instead I post an issue and the cause/solution immediately as well, hoping that it helps others.

This issue looks this way in a CoreXY printer, on a Cartesian printer you probably have only one axis looking weird.

The top part of the image has two printed objects in it, they’re corner blocks for an enclosure I’m making. The right one has a bend in it. The toolhead would consistently move 1mm to the right or left at the exact same location. Normally a layer shift occurs due to warping or loose belts or hitting the infill somehow.

The left block is what it’s supposed to look like.

Upon closer inspection of my belts it appears that one of them was stretched a small amount. These are cheap generic belts from Aliexpress that did last quite a while but were probably not the highest quality. At some point the filling material breaks and the belt stretches by a small amount. When that part of the belt goes over the stepper motor you get a layer shift.

Now I got Gates belts and hope that they last longer.

This is an article from 10 years ago but so far I have not seen any 3D printers actually use this.

Currently I’m designing a new toolhead for my 3D printer and I want to make the footprint as small as possible to maximize the usable print area. I’m redesigning an Ender 5 so that the bed of an Ender5Plus fits into the frame of the Ender5 and that most of the area is accessible by the nozzle. The toolhead is one obstacle.

My current toolhead has two 5015 blower fans, one on each side, and they add a significant amount of bulk to the toolhead. The fan ducts are also quite bulky.

Have any of you tried a small aquarium pump with a length of Bowden tubing and perhaps a blunt syringe tip at the end? This way you can precisely direct airflow to the plastic flow and not cool the nozzle down too much, which is unavoidable with blower fans.

I’m thinking towards those cheap 5v USB aquarium fans that you can buy for a few euros from China.