Very weird... smoke in the house

Had a ton of coals that I shoveled out earlier today... just put a fresh load of dry wood in (packed). Can back to the stove, and notice smoke coming into the house from where the double wall black transitions to the double wall stainless (at my cathedral ceiling support box). What could possible cause this? I ran outside to see if there were any flames or something weird to indicate a chimney fire.. but nothing.

I took a few pieces out and whipped them into the snow.. everything seems OK now? I have yet to experience anything like this from this chimney. About 9' straight shot up from the top of the stove, then straight shot out the ceiling through class A up another 6 feet or so.

Give me some insight guys. Spooked me a bit. Glad I was in here with my wife and saw it. Thanks

OK... so I think I figured it out. My wife said that while I was out of the room she head a metal on metal thud... not a clang like you hear when two pieces hit, or when the stove is expanding with heat. I racked my brain, and decided to check the ash pan door one more time. Welp... it was not secure. The damn outside air kit part that bolts onto this Rangeley has rubbed since day 1. You have to triple check that the door is locked. I guess I only doubled checked tonight. It is a good design, that I think they tried to save some pennies on (they really need 2-4 more threaded PEMS on this to secure the front most part up against the belly of the stove).

So I probably sent some flames licking up the chimney, and maybe the pressure differential (From now drawing air from the house, versus strictly from outside) caused the smoke to billow out of that joint)? The flames in the box were up the sides of the wood, and not the front (which I did think was weird).

Still looking to see what you all think. Thanks

I got up on the roof first thing this morning and took a look down the chimney... well it wasn't a chimney fire. The pipes looked awesome, with just fly ash in them. I took it upon myself to install the last 3' section I wanted to put up there, and run the roof support bracket in place.

Came in and disassembled the double wall black around the transition, and everything was tight. I am 99.9% sure it was a pressure differential now (As we run an outside air kit, and were suddenly pulling air from in the house with the ash door cracked).

Just now restarted the first fire of the day, and watching closely... but everything look A-OK now.