You had an
Auger Fire
Sounds like several possibilities… the smoker is not level or your fire pot is full of holes or excessive ash and the pellets are not dropping in like they should but are being held at the auger edge due to excessive ash buildup or an unlevel surface underneath the smoker. It causes the pellets in the auger tube to burn back because they can’t push forward anymore. Always the smoker should be at least level if not canted so the firepot is below the auger.
Even if clean beforehand, pellet choice, ambient temperatures and humidity and dial set temperature could fill it up with ash faster.
Additionally, a full hopper provides sufficient back pressure to keep most of the smoke flowing towards the barrel. Keeping your hopper full and its lid closed and that will prevent the smoke blowback.
Also…. If your hopper is smoking after shutdown, you’ll want to ramp down your dial temperature to 200° for a few minutes before turning it off. If this wasn’t in your manual then it should be.
At higher temperatures you need to ramp down your dial temperature before shutting down. It allows the fire to cool and burn off all the pellets in the firepot and not catch those in the auger.
What to do to fix this?
Whenever it happens, use the prime button to push the burning pellets out of the auger.
If you don’t have a prime button, open the lid so the barrel temperature will drop and that’ll activate the auger to push the burning pellets out of the auger.
Call Cs for a replacement firepot.