Havne't read the whole thread, so maybe not helpful ... but if I feel like there's a lot of debris in that area, I just pull the catalyst, and then it's very easy to clean out. Just need a new gasket for it, but not too bad if you buy a 10ft roll: https://pellet-stove-parts-4less.co...-x-1-16-acig-2-inch-12?variant=43407332671660Not sure on the inserts but on the freestanding stoves the bypass only opens a little ways. Meaning an open bypass does not mean that all of chimney sweepings will fall into the firebox. Only a small portion make it into the firebox through the bypass opening.
But yeah, it was my imagination.