Better pics would help. Including pics from the drums as well.
Bottom line, as close as I can tell, this looks like the friction lining sheared off the brake shoe table. It's hard to conclude from the one pic, though sure looks so.
If this is a shear, I wonder if it would be warranty?
Either way, bonded friction (glued) would be a poor technology for the weight of these rigs. Not to mention the variation in weight from side to side. (Not sure about your floor plan, ours has a kitchen slide on the road side with a door, dinette and pantry on the curb side).
Sorry for your troubles, though thankful you found this failure.
Like John and several others, we upgraded to Kodiak Disc brakes. That would be my recommendation to you.
David & Cathy
2015 Trilogy 38FL
2016 Silverado 3500HD DRW
Trailersaver TS-3 Hitch on B&W Platform