It could be related to a problem I am having with the floor and ceiling slabs.
I believe this also affects composite walls at the edges of your sections/elevations.
Are your walls composite walls?
If so try changing one to a regular solid or vectorial fill and see what happens.
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11