This happened with the ETS client, PetPeople. They own PTs and two item#s weren’t dowloading via the PT into any document. The problem was an errant UPC in another item. When the item was downloaded with the leading zeros it was conflicting with that other UPC. To find that conflict I had to type the item with leading zeros into a receipt and note what item came up on the ALU/UPC window.
Once I removed the conflicting (& errant) UPC everything worked fine.