Go to the BP_PlayerInventoryComponent then go to the UnequipItem function and change the 1 to a 0 on the highlighed nodes shown in the image below.
SGK V1 – Fixed equipping backpack with 1 slot deletes items
Go to the BP_PlayerInventoryComponent then go to the UnequipItem function and change the 1 to a 0 on the highlighed nodes shown in the image below.
Defuse Studios 