Accidental chicken jerky??

Hey guys (and gals). Long story short, wife picked up an mes 30 for Christmas and I reluctantly kept it as I'm normally an offset charcoal/wood guy. But I liked the idea of set it and forget it. Last night was my first smoke on it. After an initial trial run I noticed a 20-30 degree difference between the smoker temp gauge and my maverick dual probe. I set the smoker to 215 which maintained 225-245 on the Maverick, started my amazn pellet maze and threw on some chicken breasts and a roast. Idk what the deal was, but it took 5 hours to get those dang chicken breasts to 165. 5 hrs!! By the time the chicken hit 165 they were more like chicken pucks. A jerky of sorts. Waaaaay dry. The roast finished in about the same time, and I pulled it off at 144, wrapped it and let rest. It was juicy and tasted great. But I cannot for the life of me figure out what went wrong. The only thing that makes sense to me is maybe the smoker temp guage is more accurate and the Maverick is off, which means I cooked at much to low a temp for far too long?? Idk. Any advice would be appreciated.