[Weird z axis behavior]

The problem was dust on the filament. The problem manifested in horizontal lines, that seemed regular. Probably the dust on the filament was so thick, the clogs happened at regular intervals.

[Weird z axis behavior]

So the problem appeared to be dust. Adding a simple dust filter resolved the issue.

[Weird z axis behavior]

So my ultimaker shows some weird behavior in z-direction. Every tenth layer it underextrudes one single layer, before printing just fine. This results in prints as seen in the picture.

It seems to be caused by the z-stage, maybe it lowers to much each step, causing the evenly distributed pattern.

Could someone please explain me what happened and how to fix the problem.