[OPEN] [CD] Cats can't use the litter boxes

Product: The Sims 4
Platform:PC
Which language are you playing the game in? English
How often does the bug occur? Every time (100%)
What is your current game version number? 1.46.18.1020
What expansions, game packs, and stuff packs do you have installed? All of them!
Steps: How can we find the bug ourselves? I have tested this in a completely New Save without Mods. 1. Have a Cat in your household at ground level. 2. Build a simple room of any size (minimum 2x1) 3. Place Stairs heading to the roof of the room (to the next floor, just a way to reach "upstairs") 4. Place a Litter Box/Pet Bowl on the top floor in such a manner that it can be accessed by the Cat after it walks upstairs. 5. Find a way to drop Cat's Bladder/Hunger Motive. (I'm sure you guys have enough debug tools)
What happens when the bug occurs? The cat simply stays at ground level! The cat might go upstairs for other reasons (in this case, to sniff the litter box, to follow another Sim, maybe it has the Curious trait etc.), thus making the litter box/pet bowl "detectable". That doesn't count. You should pay attention if the cat happens to go upstairs and just sniffs the litter box instead of using it. If that happens, it may use it afterwards, for they are now on the same floor. The direction doesn't matter! If you place the cat upstairs and the litter box/pet bowl downstairs, the cat will still be unable to detect it. Again, it might go downstairs for different reasons.
What do you expect to see? My point is that the cat should simply path to the Litter Box/Pet Bowl like humans do with Beds, Toilets, Showers and almost anything (I suppose almost). I had numerous cases where my cats wouldn't go upstairs/downstairs for a different reason (like following a sim) and stayed there until they had a bladder issue on the carpet.
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 

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I have attached an image to show the simple "contraption". Notice the puddle behind the Sim. The cat was not able to detect the Litter Box upstairs and had a Bladder Issue.

Regarding the time I encountered this, I had bought the Cats & Dogs Expansion Pack around May, and have encountered this problem ever since. I am really surprised that nobody has mentioned this bug yet. I've seen people complaining about their Cats and Dogs not being able to Go Potty, but now I think I've covered much more detail that I hope you understand. I've started to suspect this around the start of July. Now I am completely sure this is what happens.

As a side note, I know you don't support Mods but, while trying to troubleshoot, at one point I have downloaded a Mod that made me able to Play the Pets. In the Needs/Motives Tab, the click to auto-complete works when the litter box/pet bowl is on the same floor, but doesn't when they aren't. Again, I have also tested this without any mods beforehand.