@sunddee4 Thanks for the extra info. Yes, I did mean changing the graphics options in the Sims 4 gameplay options. You did try with different setting so that's probably not it. But from what you said about accidently changing the resolution setting, I wonder if that could of been a trigger somehow. It shouldn't but you never know. Reason I say that is, on my last computer, my vid card died, and even though I replaced it with a better card, I could never get the Sims 4 and a couple of other games to run right again. They just kept doing weird things and I started getting a lot of crashes whenever I tried to play them. In the end, I think that the video card dying probably caused damage to something else but not enough to make the computer die outright. Ended up getting a new computer after months of trying to fix it. But I really don't think it is the cause of your problem.
So I'm back to thinking it may be CC related somehow. From what I can tell from the pictures, the shape seems to be the same wherever it shows up and it looks an outline of something very specific. In your initial post, you said that you'd removed all your CC and mods. Have you still got them out and are you sure you got them all out the first time? I've accidently put a few things in the wrong folder more than once myself and had a devil of a time finding them later on when I wanted to remove them. Also, if you installed the January 16 patch, UICheats is causing problems with build mode after the patch so you'd need to update that if you use it. That patch also caused some weird stuff with certain ingame floors too. From what I can tell from reading those posts, cc and mods seem to be playing a role in who has the problem and who doesn't but sometimes not. Take a look at some of them. Maybe one of them will strike a chord with you and give you an idea to try.
Like I said earlier, CC can cause some really weird things to happen in the game and even after you have removed it, there can still be after effects, especially if it was modded to affect game play somehow and altered how the game works and affects something that gets included in the save itself. Sometimes taking them out doesn't make a difference if it already damaged the save somehow.
At this point though, I really don't know if anything else I can suggest will be helpful to you but if you still have any questions or ideas, I'm around here often and will help you if I can.