I have almost every pack and I have populated almost every area, all set on full AI and with 'Unlimited Sims' in the game (which I assume means NPCs). A lot is going on! I am not sure if it was after the last patch or after I installed Werewolves it began to happen. I don't have round walls. It sort of reminds me of earlier versions of the Sims, that if a task given to them was a long way off they timed out and forgot they had been told to do it! But it's not that because most other tasks work ok, even in my huge houses and lots. Thankfully if I tell a toddler to go to bed, it does.
Oh, Clipping seems to be off as well now. Often when a Sim is going somewhere in a building it will walk through a door frame, or try to, then sort of revolve through the door hole, or walk along the foundations of a wall, very very slowly, as if they are actually walking a solid structure! Sometimes these strange bugs can be amusing.