Ideas
I'm having this same issue, except my lot was never a residental rental. It was, however, a retail lot, in which my sim fake-lived on. I've tried all the usual things, bulldozing and replacing, moving sims in and out and so on. It saves all the small business settings when I do this, as soon as I try to change it to one, it recognizes the layout I had before. My sim as well is in a new household, since she can now fully live on her own there. However, no matter what, the lot won't let me use it when I try to create a small business. (I haven't tried moving lots or worlds as there is no space - I have a fully custom world finished, so this lot is where it goes). I can lay out where the public and retail areas are and so on, but the small business tab doesn't seem to see it.