I am also facing similar problem where all my drawings in draft mode are appearing blank and the lines appear black or non-existent. Only the name plate of the drawings are appearing and all border/bounding lines are invisible too..
I upgraded from PDMS 11.6 Sp5 to 12.0 Sp6 and my design and isodraft module is working like a breeze. Do I need to rollback and use my backup and do the upgradeMac procedure again or is there a fix for it.