When Picking Up a Item In Your Inventory With The Cursor, It Will Lag Out Your Game a Ton If It Has Lots of NBT Data Such as a Shulker Box Filled With Items.

While Playing on My Survival World Recently, I Noticed That My Computer Would Lag a Lot When Moving Shulker Boxes In My Inventory With The Cursor. This Effect Only Lasts While Picking Up The Item. This also Happens With Things Such as Structure Blocks When Having NBT Data Saved While Using Pickblock.