Sorry i guess i should have read your follow up post. Decra may have an issue with the direct to deck application over a granulated surface. If the back of the XD gets scratched from the granulated I&W that can rust the back of the panel when condensation forms. They don’t require high temp underlayment, but they may not like the granulated surface in contact with the back of the panel which is coated, just not in granules.
They could have run a layer of synthetic or Versashield over the granulated to protect the back side of the panel. I would never install metal (Standing Seam or Any stone coated steel) directly over cap sheet or any other granulated surface product without a layer of synthetic or Versasheild.
Looking through the Decra XD SHake install manual, it does show a roof over comp but it has pink ish paper… most likely Versashield. No specific note saying it is required, but i suspect Decra would want a separation layer. The Versa Shield is also required by Decra for a class A assembly so you get your separation layer and Class A.
Donl - i have yet to see it with I&W here in so cal, but we do get some tobacco juicing from modbit on occasion… maybe a call a year.