Foundation Over Lowered Terrain Disappears

So I am on PC, and I am trying to build a castle with several decorative moats. I do not have mods, nor have I ever used them. I recently cleaned my computer (cookies, cache, etc). I even went in and deleted cache and the others in the Sims 4 folders itself (Sims was running heavy and I could not figure out why, so I did a cleanse). This issue began about a week ago.

So far, I have not added water. I have the terrain built and the general outlines of buildings created. I have walkways created. The terrain is lowered to 1 basement level down, with two floors below (but not under the moat areas)

However, when I go to fence in the walkways, closing the fence creates a floor. Upon deleting the floor, the foundations vanish.

I have tried rebuilding sections at a time to no avail. I cannot get the foundation to reappear. I have even scrapped the project and started over. This is my third attempt to create this. 

Any help out there?