idk whether this had some purpose or not but when toying around with shulker boxes with another mod that needs exact NBT data I eventually came to the discovery that an unnecessary X Y and Z data tag is added under the BlockEntityTag for no reason and it seems to be an issue; especially if for whatever reason you need to use NBT data where this inclusion can make it a pain

please look into this, and thanks in advance ^w^

data before adding item into shulker box though right click fuction

data after including item though r-click function