Alaska ChanningIII With Factory Direct Vent ...Hopper Fire

Thought maybe I could get some advice from some other Alaska owners. I am not sure what I am doing wrong. This is my 5th season using this stove and have not had this problem until the end of last year. I know this model has a reputation for hopper fires through reading many of the posts on here but never had it happen to me as I would never let the hopper get low enough to worry about it. Stove was just about idle...the hopper got low, was refilled and sure enough woke the next morning to a hopper full of red coal in the center. Shut it down, opened all the window and cleaned it out.
I wanted to test fire it now this season to be sure I didn't have the same problem. Before I did I spoke to someone from Alaska who told me how to adjust the draft on the direct vent by moving the collar of the direct vent unit behind the stove by an 8th of inch at a time toward or way from the stove. I don't have a way to measure the draft but I tried both the direct vent right up toward the stove and by as much as a half inch back and both times on the test fire resulted in the fire visibly backing up into the chute.
I figure my next option is to empty the hopper, remove it from the stove and check the gasket seal under the hopper itself. Could this be the problem? I wonder if my automatic heat control which was attached to the back of the hopper overheated and now wont work correctly as well? Just don't really know what my next step should be.
I know there have been other posts on here about Alaska hopper fires but non that I can think of with the direct vent unit. Any advice is appreciated.

The only time I had a hopper problem--wait for it--you answered you own question---hopper gasket--gets scarey don't it--I haven't had any problems since replacing the hopper gasket on my HITZER 50-93 other then I replace that one gasket every season--I'm sure I don't really need to BUTTTTTTT--rather safe then sorry A hopper gasket is a hopper gasket no matter where it is located--I doubt if your thermo will have been effected--

Replace the gasket at the back of the grate and use furnace cement to seal it making sure that it is smooth so the coal does not hang up. If your fire extends above the area where the holes are then you do not have a tight seal and you will have a hopper fire. I did

With out knowing what your draft setting I'm just guessing, but it is very likely that the gasket on the back of the grate has failed. You should replace that gasket anyway after 5 years of operation. However direct vent stoves with out the baro aare much more prone to having hopper fires than any other type of stove venting type. So fix that gasket on the back of the grate and check your drat with a manometer.