In a world (~80 MB), I've recently noticed large sections of the world have randomly moved down by 1–5 blocks. This doesn't seem to affect underground, only the top layers of blocks. Areas I have built in haven't been affected, but I often notice when updating a map etc that sections around the edge are refreshed.
Video of this: https://drive.google.com/file/d/1IJbVldlv907w-jpLy-Glk3unOLWaEu79/view?usp=sharing
This is probably the result of these chunks being saved in different versions. Chunks that you view or visit but do not modify are not saved and may generate differently in different versions.