back burning into auger

[RAYJAY]

did a long cook over the weekend , 6 hour porkbutt and did chicken thighs after, about 10 hour burn in total. did vac out and clean the 850 before i started, any ideas why the back burn ( smoke coming from hopper)

 

[HuntJ08]

I have had it happen before. Mine did it when I finished cooking and raised my temp to 400-ish to "burn-off" /crystalize the remaining grease on diffuser.
Simply, turn unit on and push prime button to force more fresh pellets thru the system.
Let burn normal for a few minutes.
Then power off and start the shut-down process again.