The only auger tube fire I experienced with my Traeger Lil Tex was when I finished cooking steaks on high and immediately shut down the grill. The "fire" actually made it to the hopper. I say "fire" because there were no real flames, just smoldering pellets. About 10 or 15 mutes after shutting the grill down I had white smoke billowing out of the pellet hopper. The cause is an abundance of fuel and heat in the fire pot and the end auger tube being in very close proximity to that fire and heat. The pellets at the end of the auger tube are ignited by the pellets in the fire pot. Because the pellets in the fire pot are extremely hot, even with the fan shut off, you get natural convection where the heat rises naturally and comes out of the chimney and fresh air is pulled into the grill through the auger tube, just like a stick burner operates. The pellets in the auger tube slowly burn towards the hopper. Grills that have a chute or something that separates the end of the auger tube from the fire pot have a much, much less chance of an auger tube fire. Also a shut down mode severely reduces the chances of an auger tube fire.
Ways to minimize an auger tube fire.
1. Drop to a low temperature, i.e. smoke mode, for about 15 to 20 minutes before shutting down. This burns off the excess fuel that is piled up at the end of the auger.
2. Use the shutdown mode if you have one. It burns most, if not all, of the fuel in the burn pot.
3. Open the lid when you shut it down. This allows the heat to escape much quicker. The faster the heat is removed from the fire pot, the quicker the flame fizzles out. It also adds a new source of fresh air so fresh air being pulled through the auger tube is minimized.
4. A full hopper will reduce the amount of air that can enter the auger tube via the natural convection. Although I think it is helpful, I don't think it is nearly as important as the other 3.