So, I had a "stink event" here to this afternoon. I was sitting in the basement, stove in black box mode (Tstat about horizontal, i.e. more or less midway in the swoosh), flue temp around 450 F (don't know the cat gauge, but it was glowing - could see the light on the haze on the window). 2.5 hrs into a burn (of a "baby load" because the 16 hr load of last night was done, and I don't want to have to reload in the middle of the night, so I try to add as much as I need to get to a good time for an evening reload).
Suddenly a nice blue/orange secondary explosion lasting about 5 secs. Just one.
I heard a "tang" behind the stove when it happened. And after a minute I smelled some "smoke". I wonder if the sound is due to the flapper being pushed open from the shockwave.
I wonder how often smells happen because of this happening every now and then - and you need to be there to see it happen. If you don't see it, enter the room later, and smell something, then all the horror stories are remembered. One might start and smell the gasket with a cone and feel confirmed it's the door because one can smell something. But it may simply be back puffing that happened when it wasn't observed. The smell can linger a long time, especially if only convection spreading of heat is happening in the home. (My fan was off because I was on a zoom meeting.)
I've seen a lot of such beautiful light explosions, and heard the clang when it happened. First time I smelled something.