I have a Minecraft world in which there are many days of work. When I joined the world in the evening, it was suddenly completely destroyed. I don't know how to describe it. I have uploaded a picture. Is it somehow possible to make the world normal again / like the day before?
Is your PC memory full / almost full?
No
But you played in 1.15.2 from the start, didn't you? If not, that could be the reason.
Played in 1.15.2 from the start