Problem:
Witch huts don't have witches in them when playing with high render distance.
Why:
Well, they have, but only for a short time because when the witch hut generates, it is so far away that the witch despawns.
How to solve:
Add the same tag that renamed mobs have that keeps them from despawning to witches generated in witch huts. That way, they will never despawn just like renamed mobs and when you find the hut there will be a witch in or somewhere around it.