This bug has been fixed in my game for a longer time now.
I also had a sim get stuck and unable to exit the pool.
This one was on ground level with no foundation. The sim had autonomously decided to go swimming and when I tried to get him out, he swam to a corner and then stopped. I was unable to cancel his actions which were greyed out trying to be cancelled. After about a minute he moved a bit but was still unable to get out.
I don't have a save of it unforunately, as I was so freaked out that I'd never get him out, I abandoned the game and reloaded from an earlier point.
Previously to this, I hadn't noticed any problems when I've manually directed a sim into the pool to swim laps. They were able to get out of the pool by climbing out from the side. The pool even has a ladder now. But it didn't before my sim got stuck... maybe I should try removing the ladder next time it happens.
