That shiny streak is a real pain. Was the bone folder wood or plastic? Sometimes the plastic ones can get a weird friction burn on synthetics. Maybe a rounded wooden spoon handle could work, but you gotta test on a scrap piece first.
Ugh, that shiny burn mark is the worst. Did you try the wooden spoon trick on your scrap piece yet? I had a plastic folder melt a tiny bit on some coated paper once and it left a permanent gloss smear. Now I keep a sanded-down chopstick just for tricky materials.