i have no idea on how to reproduce the issue but basically one of my players was just trying to move their shulker box and it crash he then mention that it dupe the shulker box
EDIT: after looking to the issue a bit more it seem that the player was using Thaumcraft focus plan and dislocation to move the shulkerbox but it seem that he had place an item inside of it before he moved it im unsure what that item is.
Version Information
Minecraft: 1.12.2Forge: 14.23.5.2814Iron Chests: 1.12.2-7.0.59.842Report Information
i have no idea on how to reproduce the issue but basically one of my players was just trying to move their shulker box and it crash he then mention that it dupe the shulker box
EDIT: after looking to the issue a bit more it seem that the player was using Thaumcraft focus plan and dislocation to move the shulkerbox but it seem that he had place an item inside of it before he moved it im unsure what that item is.
Steps to Reproduce
Crash Log
https://pastebin.com/raw/LUWVF6Bm
Forge Log