hi there,
what a strange problem!!!! sorry, can't offer a solution, only the following observations (which you may have already noted):
the section of the angled wall seems to only show part of the composite fill...but...it is somehow offset so that you see the LHS layer of the composite but it appears towards the centre of the wall thickness...
seemed to maybe be a corrupted composite element because when fill of angled wall changed to standard type fill, section shows OK...but...
adjusting the angle of the wall (to say 45°) and the section is as it should be...however it appears the problem only occurs within a defined range of angles...
therefore, not composite, not section, no hidden SEO operators, no other noticable settings problem...
very strange!!!