I don't know exactly was is happening, but the item NBT tags doesn't work any time I used them.
I've created an item that you can attach to a block, and then execute it from far away. The item should save its coordinates but when I try to execute it shows the message of non-attached that I put for these cases. I tried some other stuff with item NBT Tags and doesn't work, neither the (+NBT) thing shows up (I don't know if that should show up but doesn't show.)
Here I attach the procedures:
Issue comments
I have found the bug. The issue is that now MCreator by default copies the provided itemstack to a new stack due to some other issues. This causes that set nbt tag procedure sets it on the copy and not on the original itemstack.
I will revert the behavior so by default itemstack is not copied but referenced and require explicit copy for cases where copy is required.
This bug will be fixed in the next update. Thank you for your bug report.
There are two cases where NBT might not work as it should