Look at the fire pot before you vacuum. Are there fresh pellets in there? Some of the algorithms for the pits will pump a small handful of pellets into the firepot after the shut down procedure is complete as is done with RT grills. Those are there for two reasons:
1. to make sure that the smoldering pellets in the end of the auger tube are expelled at the end of the shut down cycle.
2. to make tinder for the starter to work on when you start up again.
So if you suction it out after every cook (not really nec. with most of the units), you should put back a little pile of pellets around the hot rod for the next startup.
Also, when the fan goes off, and the auger turns a few times at the end, those pellets also help to suffocate those few embers that remain in the ash. Not sure your pit works the same way. Easy to find out by getting the grates, pan and deflector out before the shut down is complete. If the fan goes off, and then the auger starts up and delivers a little pile of pellets, ==there you have it. Would like to know if that is a good solution for you.