3D Print Problems

https://www.simplify3d.com/support/print-quality-troubleshooting/

Pillowing

• https://all3dp.com/2/3d-printing-top-layer-problems-easy-fixes-for-pillowing/
• https://rigid.ink/blogs/news/pillowing-stringing-and-splitting-what-they-are-and-how-to-stop-them
• https://www.raise3d.com/pages/holes-and-gaps-in-solid-layers

Undextrusion

See e.g.

• https://www.raise3d.com/pages/extruding-too-little-much-plastic
• https://ultimaker.com/en/resources/21477-how-to-fix-under-extrusion

in my case it happened when I set the Filament settings in the marlin menu with "E in mm3" to 1.75. This was a misunderstanding that lead the software to assume my filament was flowing faster than it was. After switching the volumentric value off things were much better.