You may have gotten a bad spool chuck have seen it once efore where the store let it sit in the back forgotten for a few years and itll snap like that but the way you described it was your not slipped to certain poin and then the pressure broke it. Just to let you know as well I HATE the clinch knot. i lost to many off of it and tied just like the book said. The uni knot has worked much much better for me and it is all use now except a bimini twist and the surgeons dropper loop.