I've created a model with Fusion 360, and it seems that Simplify3D does a slicing mistake. The model has a few holes, and S3D fills these wrongly with a single layer thick bridge. The Makerbot Slicer and Cura don't have an issue - they also don't report an error. I also checked with Blender, if the mesh has manifold problems, but it seems to be clean. What's going wrong here?