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
So I downloaded this building off of the gallery, and I've been spending the last few hours trying to make it into something fitting the magnolia promenade area and I added this room to the back but whenever I try to do anything with the room, moving the room, raising platform to match the parallel room, or any attempt at removing the room or removing any walls with the room, my game then goes into a frozen state where I can't place items or interact with anything in build mode, attempting to save makes the game infinitely load and attempting to exit the game or save quit is met with the same issue, only task manager ending Sims 4 closes the game. I saw a few posts regarding a similar issue from years ago and recently, I do use mods but on this specific play through I wasn't using any, I've tried clearing cache and fixing integrity of game files as recommended but nothing yet, I was using the bb.moveobjects but having it enabled and disabled doesn't seem to change anything and the game still freezes,
For whatever reason the game wouldn't let me edit it on the magnolia promenade without bugging out but saving it to the gallery and placing it on Hallow Slough seemed to fix the issue despite the build being the same with no changes
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