I saw this occur on a few old computers at a school in our area. Using the original pen set for the model view, rather than overriding it with black pens, seemed to fix it.
In this case, B/W output was achieved the old fashioned way, print or plot Black & White.
I attributed the problem to a display issue related to old machines with out of date video drivers and possibly even disabled user rights by an overzealous IT administrator.
Still, keeping up with AC patches is an important step.
Cheers,
Ransom
Ransom Ratcliff
RATCLIFF CONSULTING LLC
Charrette Venture Group
ArchiCAD 4.55 - 28
Apple M3 Max + Dell Precision Workstation