Prepare for the flaming. You will be scolded for pushing a fish tape through a conduit with energized conductors.
OK Dan we've all made mistakes, that adds to our experience. And experience helps us not make more mistakes.
So, what's your next move?
you will find a lot of insulation like this if the conductors have exceeded temp or been exposed to too much sunlight over time.It seemed to just a bad roll? Maybe they left it out in the weather?
All the other conductors were good and pliable.
Would like to get a fiberglass fish tape.