In many 3D CAD programs you can assign different types of materials to an object. One that can cause problems is transparent or opacity type materials or textures. If these are set to be less than 100% opacity
then Z print won’t exactly know what to do with transparent faces. In some cases it won’t make a difference as long as the object is ‘watertight’ but in other instances it will cause the 3D model to be missing faces and not come out in the print or even cause anomalies in the print.
This picture shows an object with 30% opacity.
This picture shows an object with 100% opacity
A good way to make sure the model prints correctly is to turn the opacity of transparent materials to 100% or simply delete the features of a model than are transparent such as the windows on a house.