Old maps get corrupted when opened in 20W17A

Put the summary of the bug you're having here

What I expected to happen was...:
I was expecting to update the map of my world

What actually happened was...:
The map looked like there were holes everywhere

Steps to Reproduce:
1.first load a world in 20W16A
2. Next, open a map and fully load it
3. Finally, run the world in 20W17A and open the map