Ah, glad you brought this up! Funnily enough, I've been having the same issue lately, especially with "fancy" staircases (I've been getting creative as I get better at building). I couldn't figure out the issue--there was nothing in the way or anything at all. I actually got so frustrated with my new staircases never working that I joined this forum to ask about it haha, but I'm glad I did.
In one house I built, the stairs FINALLY started working again (yesterday) when I moved them away from the second floor railing, deleted the floor and re-added the railing, but another house I just ended up building again without fancy stairs... :/
Glad I'm not the only one with this issue, but yeah I hope something gets fixed in regards to it. I don't like teleporting my sims upstairs