I use FreeCAD 0.18.4 and have a case of a STEP-file which causes an error while importing.
I created a certain mixer geometry and saved it as a STEP-file. The import in FreeCAD fails and creates strange shapes. This does not happen, when I save and import it as a BREP-file.
When I save the geometry from FreeCAD as STEP-file and try to re-import the geometry, the same error happens.
AutoCAD Fusion 360 has no problem with reading the STEP-file correctly. The same goes for the shaper module of Salome. Only the old geometry module of Salome has the same problem.
I am not sure, if that indicates more a problem with the used OpenCascade or with FreeCAD itself. For that reason I included the geometry files and pictures of the results.
I really hope this example can help to trace down the cause of this error!