Could not find this in a search.

Explored maps, stored in item frames, have been deleted from those frames.

What I expected to happen:
Expected to look at my 4x3 map on the wall and see all the maps that had been put there.

What happened:
3 maps are missing from the corner. The item frames are empty and the maps are nowhere to be found. I do not know if they somehow popped out and decayed or if they deleted out of the frames directly.