Cautionary warning... I was trying to find the old post I did tests for someone on, but I can't find it so far. Within the last year I did extensive tests on a lot someone was having an issue on with more than one elevator added, which I think can only be done via a mod (?)... or other workaround. However, bottom line was that this person had made a beautiful cinema building, and nothing I could do would fix the fact that adding the elevator(s) as they did had bugged the lot and it would no longer let a sim enter... aside from spawning at the top floor by one of the elevators. Additionally, even if I deleted the elevator sims were no longer able to enter any of the outside doors. Also, if memory serves, I think they were stuck in the building unless you were there to tell them to go home (click their home button). I am likely not remembering all of the details correctly, and if I find the post I will edit it into this comment, but bottom line, I would not recommend using a mod to add more than one elevator, and if you do realize you may have it glitch in some manner like this. Also, you may not be able to have your sim autonomously use it for entry and exit? I would thoroughly experiment with the dynamics before saving a lot like this for use.
So, with all of that in mind, I would save a backup of my game before doing any experimenting with elevators. It's also possible that it initially worked for whatever combination of reasons but that something changed with an update or for some other reason. Doing workarounds, cheats, and mods all carry the risk of something like that.
Can you roll that game save back to a previous save or older backup?
Edit... found that thread: Stairs, Stairwell, Railing Issue: Good for Toddler NOT for Adult | EA Forums - 12346493
If you can get the lot to function properly you may want to just make some type of 'faux'/fake elevator that 'looks' like an elevator (doors that look like elevator doors, etc.), with a spiral staircase inside or something. You could even make the walls on the room tall half-walls so they didn't drop to preserve some of the effect/elevator appearance. You could make the 'room' smaller with a ladder/ladders instead, but then the type of items they can carry will be restrained, so you would want an additional normal staircase for their use if they need to carry things.
