I've created an STL model in sketchup, and loaded it into Cura. The "Normal" view in Cura looks correct. However, if I print the model, or look through the layers in the "Layers" view there are holes missing from the model - lots of them. In fact, the topmost layer (and all in between) is missing the axle hole through the center of the part.
What would cause cure's Normal view and Layers view to disagree so badly? What might I be doing wrong in Cura or with my STL model?