Same problem here. I had a few precisions, so I filled out the information as well. The picture files I wanted to upload are too large, but I uploaded my current problematic WiP lot to the gallery.
Product: The Sims 4
Platform: PC
Which language are you playing the game in? English
How often does the bug occur? Unsure. It seems to happen all the time with the right criteria?
What is your current game version number? 1.80.69.1030
What expansions, game packs, and stuff packs do you have installed? Everything except kits
Steps: How can we find the bug ourselves? Build a platform as the ground floor and build a staircase to the floor above to a large enough room that it encompasses some walls of the room below. A simmer on the forums helped me figure it out and made this video explaining it as well as temporary "fixes" that may work for some builds (turning walls into half-walls that are short enough or building a high-enough platform on the upper floor as well) : https://www.youtube.com/watch?v=nCbrAUgfx8g
What happens when the bug occurs? If there are walls on the ground floor under the second-floor room that the stairs lead to, there will be shadows where the ground floor walls are. Here is a link to the lot on which I found this problem, which I uploaded to the gallery : https://ea.com/games/the-sims/the-sims-4/pc/gallery/1F17B2A81E0611EC88DD7DB6A3FFB678?category=all&searchtype=ea_origin_id&sortby=newest&time=all&searchquery=SerraNolwen&max=50&maxis=false
What do you expect to see? No shadows from the walls of the ground floor on the second floor
Have you installed any customization with the game, e.g. Custom Content or Mods? None
Did this issue appear after a specific patch or change you made to your system? I don't know.
