Sorry, I don't know how to mark a bug resolved or indicate the version in which the bug has been fixed (these must be mojang only values), but it seems the problem doesn't happens anymore in 21w06a.

For the record, here is the original problem :

I noticed that maps on item frames loose their textures after going to the nether and then back.

However the frame is still "extended" (bigger than an empty frame)

A left click on the invisible map give it back and then it is possible to put it back.

This issue was already there in the previous snapshot (21w03a) and can be reproduced each time.