** MYSTERY SOLVED **
This has really been bothering me for the past week since the "incident". It just doesn't add up in my head. I have a 17-pound brisket, which should have required significant time in the smoker. I never went above 265° and cooked 15 hours. You'd think the brisket was under cooked and the fat didn't render completely, but the brisket came out way over cooked. Something was right.
So, I went to clean out my pellet smoker and spoke with Green Mountain Grills support. There was a bunch of ash in the bottom of my smoker which isn't normally there. That was a clue something was not working right.
It turns out their firmware needed an update. The software/firmware on my smoker was prone to voltage surges and heat spikes. The temperature wasn't regulating the way a pellet smoker should. So all the extra voltage led to all the ash in the bottom and excessive heat during the cook. Although my digital temp setting on the grill showed the temperature I wanted, inside was much hotter which would explain why my temp readings were off.
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