Ballowii

It's my first time printing and I made a Modell in Blender of a trophy which i seperated in 4 parts. In Blender when I select Non Manifold it selects no vertices and the side https://makeprintable.com wrote that it had no errors. But when I load it in Cura, it suddenly builds walls where non should be and closes a drillhole I prepared. Which settings do I have to change to stop it from doing that? I allready checked "keep open faces" which didn't really change anything. Or is this some kind of support wall, which I must cut away afterwards ? https://www.dropbox.com/s/m7et9o3uxqrpcrb/henkel.gcode?dl=0 https://www.dropbox.com/s/otas2y8oddcv85p/henkel.blend?dl=0