The issue is Duplicated from MCPE-16291
however, you guys marked it as Resolved when it is nowhere near resolved, I trapped a zombie villager in a hole at 5, 0 went to my house 140,132 to get rails to bring him over knowing despawning was not a thing, he was still back in the same hole where I left him.

When you try to make a mob farm or anything related to a big scale farm you simply cannot make anything since the mob cap is already reached from thousands of chunks you have loaded.

Seriously, like it is not cool to have to turn my world to creative and run a command block to despawn mobs

https://www.youtube.com/watch?v=ZRahG4TtqzM