When my Sim invites another Sim over (this isn't a party or a stay over, just an "invite over to current lot" on the phone), they can't always come inside.
After my Sim interacts with the guest, the "Invite In" option stops showing in the social interaction menu, and if I try to move them inside with a "chat here" action, my Sim goes in, but the guest waves and shows the "blocked" thought bubble.
The door's not locked, but I did try locking and then unlocking it. It's a haunted house residential. No mods in my game.
This time, since the guest is my Sim's boyfriend, I used the "invite to stay the night" romantic social. Boyfriend accepted, and I tried "chat here" again to move them inside. The conversation cancelled itself (this is also happening a lot recently? separate issue, though) and the boyfriend didn't try to go in, but a "cook together with" command worked to bring him inside. Not sure whether the "invite to the stay the night" or "cook together with" was what worked.