The last few models I uploaded all had various holes and other openings closed after the upload. They were most definitely open in my modeling software (I checked them with three different programs) and I have exported them as both OBJ and STL files but the problem persists. I'm looking for suggestions on how to solve the issue.
Have you checked in netfabb to see if you have duplicate faces, and to be sure your surface is closed? Both can result in mesh medic closing holes.