cura4.x
windows10
When slicing a multi-level nested model, the gaps were filled incorrectly.
Original model

Effect of slicing



the solution



It seems that this is related to the design logic of the stl file. The added bar connects the models into a whole (three independent models before this), and also helps cura distinguish the direction of the face.
This could be down to an engine issue. Please save the project file (File -> Save...) and then zip up the .3mf file and attach to this issue so I can reproduce it.
3D.zip
There are two models in the compressed package, one is not working properly and the other is modified.
Fortunately, I have n鈥檛 cleaned the recycle bin.馃槀
Thanks, I was able to reproduce it with the files you provided. Will discuss
Seems to happen in master, 4.0.0 and 3.2.1 as well, so it's not due to a recent fix/regression.
Though, if I check the model with the 'Mesh Tools' plugin (download from the Marketplace), I get the following:

We don't support models that aren't watertight or contain sub-meshes. Please adjust this in the modeller you are using.
OK,i'll check it.