Hello,
Normally in minecraft you can't stack shulkers, so there is no issue, but when you use elevators, they stack in the inventory. This cause issue when you throw all your elevators on the floor, you don't get all of them but only 1
I am using a stacking plugin (wildstacker), without it it works fine, but with all stacking plugin the issue might appear.
Exemple here :
https://youtu.be/kySb5jnPimI