Game keeps crashing or forever save screen/load screen

My game keeps crashing whenever I save an apartment or lot in San myshuno in bulid mode in the world manger. I don't know if its doing it any other worlds. I'm trying to make a forever save, so I download a save file with all empty lots, so I could place lots from the gallery and make my own townies. My gameplay is fine, it seems. My bulid mod is also just generally really laggy, and like takes forever to load search or the item by category option. But even though thats laggy it doesn't crash my game, it's just me saving my lot after placing a lot down from the gallery. 

I don't have any bulid mode mods, and all my mods are up to date, unless they are unknown but as I've said my game runs fine in game mode and I only use gameplay mods. I have cc but I unsure if that would be the issue, the crashes have only been happening with lots from the gallery with no cc. 

If anyone has any suggestion, please tell me!!