Alright I guess i just found a workaround. So what i did was i copied
the beams that caused the problems. Then i removed the old beams that do
not display correctly And moved the beams that were copied to the right
place.That solved the problem for m...
It feels like it happens when the project gets larger and I guess it
just become harder to handle a hierarchy of all the lines for Archicad,
because when I started the project from the beginning the problem was
gone.But then later in the same project...
It is in a standard library, the element's called Audience seating. But
the actual problem is much worse because you can see stair lines
overlapping and manually fixing display order does not help at all.