Fuzzy skin skip layers

Hey all!

I’m trying to print a part with fuzzy skin feature in Creality 7.21.
So I’m selecting my part, push “Paint-on fuzzy skin”, then I pick a “Fill” tool type and apply it to an outer wall (one of them). Everything looks fine:

So I hit “Slice” button and have a nice fuzzy surface EXCEPT for two layers!

Let’s take a look closer:

The strangest thing: it’s fuzzy on the rounding but flat on a flat surface. Only at these two layers.
I’ve tried to understand what makes these layers so special but nothing comes to mind.

Please note: the “Fuzzy skin” feature in settings is set to None. Here are all the settings.

If I set “Fuzzy skin” to “Contour”, these straight lines will disappear but I’ll have to strugle with holes fuzzying:

Of course I have tried to change the fuzzy skin’s options, all of them.

Please advice!

How does it look when you print the part?

It’s seen as thin 2-layer line. Very glare on certain angles.

I checked the mesh for errors; there are none, and the geometry is closed.

What helps in this situation is cutting off a microscopic layer from the problematic face (less than 0.05 mm). At this point, though, the question is less about how I can cut something off to work around the problem, and more about why the problem occurs in the first place.

If the print layer height is 0.2 mm, my understanding is that the slicer should average the surface over that 0.2 mm. Or 0.1 mm, or some other thickness—but it should average it somehow. Instead, what we have here is a model with no holes in the mesh where a tiny surface offset causes the slicing to fail. And, even more importantly, this happens when trying to hide defects by applying a distortion that is much more significant in size.

If you look closely, this occurs on the same height as the part of the object on the side…

I have noticed this kind of “banding” before… but haven’t searched for a solution for it… You could try another slicer like Cura or Orcaslicer to see what happens!