I am having a very similar issue. I have tried multiple different things to eliminate other possibilities but every time I try to delete a wall in build mode the game freezes and I can't do anything ...
Ideas
I am also having issues building walls and just general placing items, this started happening yesterday. When I build walls, the cost isn't subtracted from the household funds, I can't delete anything, the "undo" button in build/buy doesn't work along with ctrl+z and when I move items placed before yesterday they disappear and I cant undo that actions either. The items disappear after the walls have been placed, if I move them before the walls are placed, they are still there. If I buy a new item, it will be placed, but if I click it, it will disappear - the cost is also not subtracted. When I leave to either main menu or desktop the game freezes - I haven't tested if the game also freezes if I play and doesn't enter build/buy.
I am playing on a lot where there is a small business and home lot. I have tried: repairing the game, changing the lot to all public rooms, changing the lot to all residential rooms, removed the 2 mods I play with and redone the before mentioned steps
I am uploading a save file for you guys to look at