I had an air leak where the burn pot connects to the body. You could see the spike in the ash in the barrel of the pit. I sealed that with the high heat silicon. Unfortunately, I also replaced the controller to the wifi controller that had a higher firmware version and replaced the heat shield to the new one piece stainless one at the same time. I do not know what fixed it since I did it all at once, but it did stop.
I would start with the easy cheap fixes first and then move to the controller last. Both fans need to run and never stop, even when it is pulsing, they should only slow and not stop. Check for air leaks and seal around where the burn pot attaches. The pellet hopper lid can be checked also by putting tin foil over the top with the lid open, then close the lid on it. If that works, the lid is too loose.