While building an enderman farm my crafting table and shulker box full of materials for the farm despawned. I placed them both on the obsidian platform that you spawn on when you enter "the end", began to build the farm, left the end to get something i forgot, and when i came back both were gone. HOW?!
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this is not a bug, thats the intended behavior. When a player, item or any other entity crosses the portal the obsidian plataform resets and everything 3 blocks above it gets deleted. This is done to prevent people from destroying the plataform.