Wow, what a machine! New owner, go cook and enjoy!

Hi all, after much investigating and reviewing, I picked up the YS640s last week. Very impressed and love the convenience of built in temperature probes.
My question for all of you is the set temperature vs. the pit temperature. Why did my unit shoot up to almost 600° on burn in with the set temperature at 350°. It scared me and I shut it down. I decided to try it again and got the same result. I let it go and it eventually came down to the 350°. However, my hopper lid now rubs on the firebox.
My question for all of you is the set temperature vs. the pit temperature. Why did my unit shoot up to almost 600° on burn in with the set temperature at 350°. It scared me and I shut it down. I decided to try it again and got the same result. I let it go and it eventually came down to the 350°. However, my hopper lid now rubs on the firebox.