When a world generated from 1.13 or more is outdated, the world instead of eliminating the related changes, in these more current versions, regenerates the world of 0 eliminated all changes made by the player.
This bug affects the versions:
1.13 and / or +
1.14 and / or +
1.15 and / or +
20w06a and / or +
Related issues
duplicates
Comments
CubeTheThird
The bug you indicated is marked invalid, please reopen the part.
CubeTheThird
As indicated, version downgrading is not supported, which is why the other report is marked as invalid.
While not exactly the same, I will mark this as a duplicate of MC-45009. Version downgrading has never been supported.