It can be more than 1 issue. If you try to do 321 with spareribs, you have to run hotter or longer compared to babybacks. That with another one or two issues can make it an unexpected 8 hour cook.
When you clean it, be sure to put a half of a handful of fresh pellets in the firebox. You may have to reprime the auger if you vacuumed any out of the entry pipe in the fire box. I have found this makes it easier to start. I don’t know if you got to the startup process or it would not turn on.
My wife has not figured out how to pick a brisket. The entire brisket is the thinnest one I ever had. It has the same thickness including the point (1.5 to 2 inches max) which is probably good for cooking evenly. I am starting the Matt Pittman weekday brisket to have with some friends tomorrow...
I like to use Old Bay on corn on the cob. Completely Chuck the corn, smother with olive oil, spread Old Bay on all sides and smoke for an hour at 225 bare on top rack. Amazing!