Some already used maps are empty and damaged

This is for development 1.16- 20w21a.

Sorry being late with that, but because i spent my time in nether, i missed what happened in normal world.

I found maps in frames at walls and they show nothing and seem to be empty. When picking that from the wall and frame, then they get new numbers. But they now cannot be used as maps furthermore. They stay empty. Trying to change level works once, but also then they didn't work as maps

This is a problem of 20w21a only; 20w20b and 20w22a seem to be OK, others also.

Maybe someone wants to check what happened there.