Magic Storage Mod Deleting Chunk of your Terraria World Map
The Mod "Magic Storage" for Terraria can vastly increase the storage capacity of items in your game, but the mod suffers from a bug that occurs with how tModLoader handles it.
If the number of items in the Magic Storage system exceeds a certain limit, a portion of the map will appear to be deleted in your game client. The Chests, the Magic Storage controller, and an entire section of the map will appear to be gone.
This exact number of items that will trigger this event can vary from 300 to several thousand, depending on other mods you have installed. Most reports involve approximately 2000 plus items in the storage network. The epicenter for the "deleted" area is usually the main controller for the Magic Storage system (which is usually in your base, so that means the entire section of the map with your base in it will be gone).
The area is actually still on the server, and has NOT been deleted. Due to the bug with tModLoader, the server cannot send the information to your game so that it can be displayed properly. The section of the map only appears to be gone. It's still there. Unfortunately, since it's not displaying in your client you cannot interact with anything in that area.
How to Fix it?
Download the Terraria world and open it as a single player game. The disappearing chunk issue only seems to affect multi-player mode. You will be able to see and interact with the missing chunk of the map in single player. This will allow you to make changes to the magic Storage system. Break the system into smaller networks, and make sure the chests that hold the items are spread out, and not all concentrated in a single area of the game.
When finished, upload the edited world map back to the server, and make sure that chunk can be viewed normally. It might take several tries to reduce the items to a point where it no longer triggers the "deletion".
Remove the mod, and restart the server. The "deleted" chunk of your map should be restored, and all the normal chests that were on the map will be restored. Special chests or other elements of the Magic Storage system will be gone though, since the mod was removed.
Note: The developer of tModLoader plans to introduce changes that prevent this bug from happening in the future, in the next new version of tModLoader