I googled a lot and I had that problem already some month ago with a different model. I had to do it all over, and then it worked. This time, I couldn't make it work. I have a model that is 100% OK, created by Blender Beta. This is just a part of a model. I printed the whole model and everything worked out fine, but when I print only a part of this model, Cura closes the holes. I checked the "Mesh fixes" section in Cura and deactivated everything. Still the same. I did the model all over again, to make sure there are no bugs, still the same. What can I do to forbid Cura to fill the holes? The STL is attached.
Cura 4.4.1 Prepare view
Cura 4.4.1 Preview view