If you type
entitydata @e[type=minecraft:item] {PickupDelay:0}and
advancement revoke @s only <path to this adv> as reward commands in an advancement with the minecraft:inventory_changed-trigger and you "spam" the drop key for 30-60 sec you can duplicate the item. You will get a "real" item which you can use and keep after a rejoin.
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However, this issue has been closed as a Duplicate of MC-115404.
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