Hey guys, I know this question has been asked before, but I can't find any of the threads right now. I just got a call from a customer who is baking cookies right now. She is lining the bar pan with parchment and baking drop cookies on it. She had to end up baking them for 20 minutes when they were only supposed to take 8-10 minutes. I've never encountered this before. What's the deal? The stone is not new, the oven was preheated.