I have a Flashforge Creator Pro. I installed Simplify3D 3.1 on both Windows 10 and Mac OSX. I can import .stl files just fine on the Windows System, but the same STL files do not load on Mac. The software indicates that the model is too large. Once I create a New factory file, sometimes the problem goes away. Sometimes creating a New factory file simply crashes the Simplify3D. I think this has something to do with how Simplify3D loads the printer bed's STL. In another words, if I see a generic box instead of the Printer's bed on the screen the software works OK (for a while).
I guess I can only Simplify things on Windows until these bugs are ironed out.