Hi Alex, 
 
I am in the process of adjusting the priority connections, but am still getting used to them. I have listed them below so you can see what might be wrong. 
I have also updated the earlier image with the masonry wall composite now intersecting the concrete slab composite. 
 
So here, I want the inner masonry skin (BM-brickwork clay) to disappear behind the slab (BM-structural concrete), creating a step-down in the concrete slab for the outside skin. And, the slab finishes (BM-air space fixing) and (BM-Carpet) to stop when they meet the inside finish of the wall (BM-cement render). 
 
I'm not sure though that priority connections will resolve the outer masonry skin step-down, because if I change the priority of the BM-brickwork clay, both skins might disappear if you know what I mean.    
 
For detailed description of the building materials involved see below: 
 
Cavity Wall  
- Brickwork Clay - 700 
- Air Space Cavity - 702 
- Cement Render - 500 
 
Slab   
- Concrete Structural - 932 
- Carpet - 683 
- Air Space Fixing  - 620
