Exactly the kind of thing that lead me to remove the automatic feature.
I cleaned everything up, lubed the threads of the adjuster wheel with copper never seize and the contact points of the brake shoes [lightly], then adjusted the rear brakes to get them in close contact with the drums. Since I did the adjustment, not the "automatic crap" I know what I have and just made the mental shift to "adjust the rear brakes".
It works for me. If you have mama driving the truck and she never pays attention to what's happening mechanically.. check them as part of your check list. With the rears set to a good adjustment, your park brake peddle will engage the rear brakes with little travel.. as they wear.. the park peddle will go farther down to lock up. Time to adjust the rears..