The images below show a detail of a section with a slab, a beam and two walls.
The first image is what I get.
The second image is what I want: I manually added vertical black lines on the edges of the beam.
The reddish lines in the walls is masonry (priority = 510); the black lines in slab and beam is structural concrete (priority = 760).
The priorities work as expected for the fills of the elements – concrete fill goes on top of the masonry fill, but not for the contour lines of the elements: the sides of the beam are red instead of black.
Changing display order does not change this situation.
All the layers have the same intersection index.
This project was started in an old ArchiCAD version (v7, if I correctly recall). If I set Preferences to use Legacy method for intersections, the problem with lines goes away, but then a bunch of other intersection problems arise.
AC 24 BR – MacBook Pro 2,9 GHz Intel Core i7 16GB RAM Mac OS 10.14