March 2021
Okay not complaining here this one's rather funny. When you got build menu and exit out of it. My sims seem to fall threw the steps and get stuck in the void under the steps. Rather funny coming home after work walking in the house and watching your sim doing sit ups in the crawl space under the steps cause there's nothing else to do. I've actually had to leave a door just so they can get out again and not be stuck with the voices in their heads.
March 2021
I had something similar happen in a previous game when I logged in, the sims were standing in unaccessible places. Like under the stairs and mostly in the dining table. I had to shift-click and teleport them out of there. But the issue solved itself after a day or so
March 2021 - last edited March 2021
@EloquentSickness and @Lailantie to avoid Sims getting trapped under staircases I tend to remove the walls around it. This enables them to always walk away without me interfering. The shift click teleport option is one of the workarounds I used to fall back on. Besides it is a known issue and has been there for ages!. There is also a thread with the workaround: https://answers.ea.com/t5/Bug-Reports/WORKAROUND-Sims-get-stuck-behind-stairs/m-p/7924186#M91032
Have fun playing. 😉