Within The End dimension maps, blank or otherwise, within Item frames, become invisible after leaving render distance and returning. The entity is still there, as after a few seconds of removing the block upon which the map and item frame is placed, the two pop out as dropped items as they would normally if the block was removed. However the item frame and map are not detected by mousing over them. The block on which they are mounted can be removed from front.
This does not effect paintings, banners or carpets.
In summery:
-Placing map onto item frame on a block maintains normal appearance
-If left beyond render distance and re rendered in returning the map and item frame become invisible and cannot be directly selected
-removing the block pops the items out but can be done from in front of where the map was previously

the image is normal map wall taken pre update(1.12.2)
the wall is now instead simply the block types behind the maps with the maps invisible