Have a look at the Intersection Priority Numbers of your layers.
Even is a layer is hidden, if it has the same IP number as another layer then elements will interact with each other (i.e. walls will trim other intersecting walls) resulting in the gaps you are seeing in plan.
The IP number is stored in the layer combination, so be sure to set them for each combination.
If you have any layer combinations where they should interact, then make sure the layers have the same number.
In the combinations where they should not interact, then the layers need different numbers.
Setting a layers IP number to 0 (zero) will mean even walls in the same layer will not intersect.
This may also be the solution for your elevations.
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