Your issue is to do with you the
Building Material
(BM) of slab compared to your wall. They currently end at the same outside edge with the slab having a higher
Intersection Priority
(IP) than your wall meaning that it will clip your wall.
You have a couple of options depending on the detail and accuracy required. The easiest would be to chance the edge material of your slab. The second but least accurate would be to assign the wall a
BM
with a higher
IP
than the slab so that it clips the slab instead. Another option would be to set a reference line offset to your wall so that even when the slab meets to same point, the wall will extend say 5mm past to represent the wall finish. The most accurate option would be to create a composite consisting of your structural elements, with the inner wall and finish being to lowest
BM
and your wall finish then setting your wall reference line to
Core Outside
. This will create a section like Eli's.
Ling.