A recent roll of HIE of mine has a similar spotting. I bought mine at a shop in Newton, Mass, so I don't think it's a storage thing. And it didn't happen in every frame, as far as I can tell; maybe just the ones where I was out in the sun. Someone mentioned it could be from the pressure plate in the camera. I know the one I used does have a dimpled plate. The camera I used to use did not and I never had this happen with rolls from that one. Could be coincidence.