There is nothing worse than this Joe, you stop and lose the print run or continue and hope that it is accepted by the customer. even if it is replaced, you only get the replacement roll, not the wasted print media, ink, time etc! 🤨
That said, I have seen similar happening with most brands over the years for multiple reasons!
Just one of them being over tightly wound rolls. Which I see more often near the core of coloured vinyls to the point you can see the spiral card tube marking on the face of the vinyl. or inconsistent gloss, as you say, or blotching dull marks here and there.
Something that is consistent all the way through a single roll “could be” what I noticed once many moons ago, with a “dull finish-gloss finish” all the way in vertical lines (by the width). was a slightly compressed in the middle card tube core. My opinion is that whilst this would be tightly and consistently wound by a machine during manufacturing/reeling/boxing, that slight egg shape of the core means at the top and bottom of the egg, the vinyl will be “tighter” wound at those points. Creating a dull impression from the bottom of the carrying paper.
Anyway, nothing more frustrating, mate.