What has GMG had to say about this?
+1 Have you called them?
If it started that way could be the controller. Up to date firmware version?
Combustion fan working OK?
Hopper lid closed tightly?
Could be that the fire pot is not sealed completely.
Do you foil drip pan? Some say the foil affects airflow.
Sawdust from the bottom of the bag could work it's way to the burn pot, built up on the bottom and there it just smolders.
Be certain the pit is at operating temperature for a bit before putting any food on.
Big jumps in temp could cause this. When going up or down go slowly or cover food.
High grease food like chicken skin at high temp will splatter and burn on drip tray causing soot.
Do a 500 burn off after cleaning your grill. Start at 350 and slowly raise to 500 so to not start fire. Let run until heavy smoke stops.(2-3hrs)
I would start by calling GMG.
Mudflap