When crafting a map zoom, the map only actually zooms occasionally. Sometimes it will clear the map completely and requires reloading the world to start using the map again.

More info - If I manually move the zoomed map to my inventory, and then my hotbar, the new map creates properly. If I shift click it directly to the hotbar, it doesn't form a new map and often wipes the data of the map I just changed from. When I drop it into my inventory, it changes to one map, and then settles on the new map it should be when I drop it on my hotbar.

Example:
I craft a map. The game gives it map slot #4.
I zoom the map and shift click to create. It stays the same map and sometimes wipes map data.
I zoom map #4 and drop it directly into my hotbar with a manual move. It sometimes becomes the map I want and it sometimes becomes a random map I've created previously.
I zoom the map, move it into my inventory and then move it into my hotbar. It creates the correctly zoomed map I am trying to create.