I'm having a lot of troubles with my pre-existing "old worlds". I've always built in the limited world mod because i don't like unlimited ones, with the last update the world size is many blocks smaller and in my pre-existing worlds beetween 15 and 35 blocks for side became invisible, if i move the hand on them i can see that they are still there and i can also walk on them. That's frustrating because i lost a lot of houses and a lot of land. At the same time in some cases i can't even put new blocks in those worlds!
If i make these old worlds unlimited the invisible land become visible again but, as i said, i don't like unlimited worlds.