Picking up a full shulker box causes the game to go from 140 fps to 3 fps instantly. This only occurs when picking up the shulker box, not when shift clicking or navigating through your hotbar. The issue makes utilizing shulker boxes very difficult as trying to sort your inventory takes about 30 seconds to a full minute of just waiting instead of being able to smoothly move an item from one place to another. This has been an issue since the Caves and Cliffs Part 2 Release and I haven't seen any recent mentions of this problem.

Update: This issue also affects xbox consoles, as it causes their xboxs to freeze and are forced to restart the console or the game

Side Note: Enchantments on Tools also cause fps drops, but not as severe. The game drops from 140 fps to around 30 fps when picking up a tool with multiple enchantments on it.