I also have this issue, every pack except kits & batuu installed. Started happening after the patch before cottage living came out and has been happening since with staircases.
New save, no mods, no last exceptions and a repaired game. House with plenty of room to move around, so shouldn't be routing errors due to lack of space either.
Basically what I've noticed in my game is... If you queue up an action that is on another floor and then go to that floor to start queueing up more actions or just wait for the sim to come downstairs, time will pass and the sim will just appear at the spot where they were suppose to be going, seems they will pause before going down the stairs (happened to me while going up a couple of times too, but not nearly as often) and then after a whiiile has passed, they will just teleport and either resume their actions or entirely drop the queue aka. reset.
This has also happened to me with open staircases, but way more with closed ones. I think just as much if not more with shaped staircases. Width seems to also be a factor: more width = less failures. But it's not enough of a factor to be able to help solve the issue, the stairs would have to be ridiculously wide to help in a noticeable way.
Been going absolutely nuts with this bug since the patch dropped. Happens regardless of household, household size, pets/no pets or world/lot. Both in new saves and old (pre-patch).
The longer your play session is, the worse it gets.
My sims also walk through walls and fences now temporarily. Like, if there's something a little bit on the way (like another sim or an animal) they will pass it by, albeit through walls and fences and once passed by, return to their normal route. I guess it's good they don't just cancel what they're doing, but it's kind of distracting none the less. In my game the simulation lag has also gotten worse since the last update. Sims are standing around actions more, like after using the toiled before flushing they just stand there for an awkwardly long time.
Tried also adding mccc to see if I could catch any last exceptions with stairs, but none would show. Just repaired my game for the upteenth time and gonna try maybe disabling some packs to see if anything might ease it a bit.
