I've had this problem as well, I first noticed it after building a greenhouse as a separate building and installing a glass roof on the greenhouse. After doing so, I noticed in first person mode that the ceilings disappeared and I could see the upper floors.
After playing around a bit, I was able to resolve the issue entirely in my game by using the sledgehammer tool to delete the ceiling of my greenhouse before installing the roof. Installing the glass roof while the ceiling is in place automatically removes the ceiling (because otherwise what would be the point of the glass roof...), but getting rid of it before even putting on the roof resolved my issue with the missing ceilings in the rest of my house.
Not sure if this will help anyone else, but it does seem to have worked in my own game.
Product: The Sims 4
Which language are you playing the game in? English
How often does the bug occur? Often (50% - 99%)
What is your current game version number? 22.214.171.1240
What expansions, game packs, and stuff packs do you have installed? Snowy Escape, Discover University, Island Living, Seasons, Cats & Dogs, City Living, Get Together, Get to Work, Strangerville, Jungle Adventure, Vampires, Dine Out, Spa Day, Outdoor Retreat, Tiny Living, Laundry Day, Bowling Night, Movie Hangout, Cool Kitchen, Luxury Party
Steps: How can we find the bug ourselves? Build a room on a waterfront property in Sulani, go up one floor. Move the camera around (Sims 3 camera) until the ceiling flickers in and out of existence.
What happens when the bug occurs? The ceiling doesn't exist unless I hover over it with my mouse, regardless of whether anything's in it. I can see down one floor with some of the furniture (depends on the angle). You see through unenclosed areas and rooms that are enclosed by fences.
What do you expect to see? A ceiling/the floor of the level I'm on.
Have you installed any customization with the game, e.g. Custom Content or Mods? Not now. I've removed them.
Did this issue appear after a specific patch or change you made to your system? Neutral/Not Sure
I've messed around with this a bit, but it seems to only be happening on some lot and not in others, so I'm not sure if there's a correlation, but it started in Sulani on the water.
Raw screenshots are also attached.
when the mouse is not hovering over the room:
when it is (what it should look like):
one angle seeing down and another (where the furniture blips out of existence):
This is what happened to me too with the separate greenhouse. It caused a problem for me trying to do anything (add walls, create flooring, place roofing etc) on the second story of the main house. I found a workaround from another thread that said to use a normal roof (non-glass basically) while working on the upper stories, then add the glass roof last. That's worked for me so far, but I haven't had any Sims go into the house yet so I'm curious if the flooring/walls/objects will persist or become unusable because the ceiling (aka second floor) is being removed when placing the glass roof.