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 was about to finish a house i was building. then i changed my mind and wanted to turn a room into a veranda. after deleting the walls and windows, i can't put anymore walls or windows or anything. i press f1, the game cannot be 'unpaused'. i thought at first its a problematic mod--it not. i tried removing the mod and opening the game--result is still the same. the game sort of freezes. i was building on heavy mods/cc lol
to solve it, what i did was i saved the unfinished house into my library.
i then deleted the house while on build mode (without changing the terrain, just the house.) then i bought the same house i saved in the library. and it worked. i was able to delete the windows and remove the walls and continue building.
(but i still dont know why it was freezing in the first place lol ).