I think they are referring to the backdraft damper inside the air intake, make sure the flapper is moving freely. I would also remove the burnpot cleanout cover and clean out any fines & ash inside the burnpot, brush off the igniter while cleaning inside the burnpot. If the stove fails to ignite, it will purge fuel each ignition cycle up to 3 times before shutting off for a failure to ignite. If the stove ignites on the 2nd or 3rd cycle you would have an abundance of fuel in the burnpot that may have caused the loud pop when the pellets finally ignited. A burnpot full fines & ash does not allow enough combution air.

Pellethead- thanks for the response. Here's what I've determined happened:

I was doing some remodeling work in the room beside the room with the stove. I think that the floor vibrated and the stove "walked" just enough to create some small gaps in the silicone sealing the pipe joints. When the stove started up, the excess smoke in the firebox leaked out and was then picked up by the air intake and blasted through the room.

I cleaned out the burnpot and the ignitor chamber and start ups have been fine and I've re-sealed the vent pipes. My sealing job isn't the prettiest, but it'll last until summer when I can really disassemble and reassemble everything. I also cleaned out the vent pipe, but there was little to no ash in it.

I'm still really impressed with the stove- we've been using it all winter to heat our 2000sf uninsulated farmhouse and it's been doing a good job.