In one of my comments I was somehow wrong with my information about the font. I wrote: `The Font name is Liberation Mono, the Style is Normal and the Point size is 28.` That is the font of my system, but not the font of Geany. The Font of Geany where I can see the issue is: Monospace Regular` size 27.
I changed in the Prerences of Geany in Interface, in Interface, in Editor the font from `Monospace Regular` size 27 to `Liberation Mono Regular` size 27. The issue does not occur any more, in all zoom sizes.