Best Chicken I've made so far, but cracked deflector plate in the process.

Started my cooking today with Brazilian sausage at 250f. After that, I went to cook my chicken and bumped the temps up to 355f. I had put potatoes to cook directly on the deflector plates in a cast iron pan right before I put the chicken on. I noticed the left plate wasn't sitting correct and when I went to adjust, the plate just cracked in my hand. Should I have not put the cast iron directly on the deflector plates? I'm in nj and it was around 40f outside today. Not sure if that had anything to do with it either.