Apartments bug - walls misaligned

So I moved my sims into 1010 Alto Apartments in San Myshuno and got into build mode to decorate the apartment, and halfway through I realised an irritating gap between the outer walls and flooring. I've tried lowering and heightening the platforms, rotating rooms, moving and re-placing the lot, changing wallpapers etc. but nothing is working. The misaligned walls are only on the longest side of the apartment and the corner shown in the 3rd image. The rest of the apartment is fine. (I've reloaded the apartment and game multiple times, and removed custom content, didn't fix)

Packs: Seasons, Cats & Dogs, Discover University, City Living, Tiny Living Stuff.

Mods: Custom content only.