On our server we went to the end with some maps. We came back to the overworld and some of the maps displayed correctly, but others didn't.
In the player's hands they appear blank (although sometimes they have a cursor there is an old resolved issue with cursors displaying on end maps in the overworld)
-On the wall they are invisible, although they make the item frame size bigger

There doesn't seem to be a link between whether the map has a cursor or not and whether it displays correctly. (Kind of neat to make big picture frames for building details- although you can't put anything in them) but overall kind of annoying.

Some maps did display just fine. I made 8 regular scale maps while I was in the End, 3 were fine, 5 were messed up. They were all in my ender chest inside a shulker box when I left the end (well, fell out of the void... oops). The maps, if they don't work, don't work ever... ie popping them off the wall and putting them back up doesn't help. I think all of the maps were completely filled in (I know on overworld maps sometimes part of a map will be invisible if you didn't map it when you put it up on the wall. That may be the root problem- for some reason the maps we made may be 'blank' and putting them on the wall with a data error may be the cause of the problem.