Did I overcook the pectin?

So I made a really large batch of quince jelly. Quince has a high pectin content but I still added extra. Before a pressure canned them, The jelly had fully congealed. When I took it out of the pressure canner, all of them were near liquid. I only pressure can for 15 minutes but is it possible that the high heat and temperature broke down the structure of the pectin?