Ideas
Added tags. Yes it's only for a single sim, a witch with familiars. Everything else in the household continues as normal while the one sim freezes mid-step. Other sims keep doing their actions.
Oh one other change, I moved my household to a new city and the sim bug is completely gone. The household was in the empty home in the new enchanted city with the fairies. The house has a lot of half-levels/raised floors, I was thinking those could've been causing this bug or just something else about that city/neighborhood.
After moving, I had a separate sim stand around at the hospital, not moving or obeying the order to walk/space bend. But they were checking in at the front desk, although the check-in action was gone from the queue. It showed the movement actions. But they stayed above the queue, not entering the queue. The sim missed the whole birth process while standing there. This same sim had no issues during previous birth, but I didn't have them check in. I had him check in this visit to the hospital because the doctor was standing outside not following the couple inside to deliver the baby. Not clear if any sims or NPCs were frozen.