Sounds like a venting problem .Not enough draw in exhaust to remove the gasses caused by the ignition cycle .If the are not vented out fast enough ,when they do ignite it will be like a small explosion . We call that gasification ,and gas burns faster than solids .Check exhaust vent for blockage .
I had the same issue when I had my PB105. The issue was a worn out igniter. It took several minutes for the pellets to light. They just smoked and smoked and smoked and when they got hot enough to ignite all the gas that built up exploded.
I would clean out the igniter area and then try a new igniter. That should help.
I had a similar problem with a P68 on this year's first burn. Too much ash in the exhaust trap had accumulated, and it blocked the air flow pretty good. The stove did not want to light but I got it going with a gel. The flame was deep red and the smoke was really noxious. The buildup of smoke caused a small explosion, pushing the door outward with smoke puffs coming out from around the door edges, but fortunately did not distort the door. Once I cleaned the trap, it was fine.
I have seen that happen. Not that bad though I have seen air inlet flapper on back right opposite the circuit board stuck closed. It sets vac switch and stove tries to start with minimum air flow. Pf100 is most susceptible do to being installed in a basement nearly every time. Moisture makes them rust and stick. When I service a Pf100 the first thing I check is the flapper. I had one doing the same thing, smoking for a long time, I could not figure it out then I looked at flapper and thought oh that is the problem. I tapped it and it opened. Air rushed in and it ignited with a boom. Fire even shot out the air inlet flapper!