Seren:
One thing to check is Door Settings > Floor Plan and Section > Floor Plan Display > Floor Plan Display >
Symbolic. It looks like the door is not set to Symbolic, so the 3D Model of the door is being cut through in plan (using the Floor Plan Cut Plane).
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David