You've misread the no problems part, I was saying it loads with no problems (as in load errors) in the viewer I designed it in. (It's the 3D builder that comes with windows 10 so not just a viewer.) I can't see how it can be a scale problem, I have a model that is the same as this one but without some small holes I made in it and that loads in cura fine. It's certainly not scale independant, you input the size in mm (or whatever units you have set) for everything you add. What do you mean by file size, is there a limit in what cura will load?