About model and data exchange with 3rd party solutions: Revit, Solibri, dRofus, Bluebeam, structural analysis solutions, and IFC, BCF and DXF/DWG-based exchange, etc.
It happens because this is how it is in ArchiCAD. Just sanitary elements have white background, that hiding fills below. AutoCAD is not showing this background.
If this hatch is coming from zone - you can safe only zone stamp without the fill (see DWG/DXF conversion settings).
