Top layer of chunks disappears

Since the last update the top layer of random chunks is disappearing when saving and reopening a world. I used this world for a few months and leveled quite a big area.
At this area the top layer of random chunks is disappearing. As soon as I fill them up again, save and quit and reopen the game different chunks in the area are affected.
I duplicated the world only to find that the same problem appears here.