So I made a world in 1.14 two years back and loaded it sequentially throughout these years in 1.16.1, 1.16.5, 21w43a, 21w44a, and finally the 1.18 pre-release. Everything is fine, except that whenever it rains, it goes through the roofs of any structure of build generated or made in old chunks loaded before the pre-release such as trees, village houses, and so on. It even rains through water! I can temporarily fix this by removing and replacing the block the rain goes through, but doing that on a large scale will not be worth it.