When a item is summoned with the PickupDelay tag set to 32767, any matching items that can stack up to the stack limit will join the stack and be unable to be picked up again.
MC-47543
Items stacked with Items that have PickupDelay set to 32767 can no longer be picked up
Resolved
Fixed
0
This problem is bigger than just the PickupDelay tag. I have created another report (https://bugs.mojang.com/browse/MC-47596) to show my findings