Smoke like burning paint from top of heatexchanger

The fire got really hot for a while like a blast furnace and smoke (not pellet burning smoke) was blown out from the area over the heat exchange tubes smelt a bit like melting plastic or overheated stove paint.
3 or 4 years of burning without problems.
I am wondering about that sheet of faux brick material covering up something just behind the firepot which has a cutout to allowfor the auger tube discharge into the fire pot. Is it supposed to be changed once in a while?
Maybe it got hot on the hopper wall
I gave it it's midwinter leave blower on the chimney treatmeant last week and its been real good
maybe it nothing. I have it shut down now and will have a look in a half hour or so
Not many of these stoves around as depicted in my Avatar, it is a Canadian Tire imported Quality Craft 2800

Cleaned some dust bunnies and figure maybe that was the issue,
new gaskets next season

I spent some time cleaning the 1/2" clearance space between the hopper and the heatexchanger. Got some greasy dirt out accumulated dust and whatnot.
the overfire I think caused by an abundance of short pellets in these west coast pellets
It's going nicely now and behaving normally thanks for the response btw

yes I did get into it and sucked out a fair bit of stuff. Jeez yeah if it blows gunk into the tubes then maybe thats what was smoking . Dog hair, dust and who knows what else. What it smelled like alright