Trailer Electric Brakes shudder at low speed....Why?

I guess I will remove drums and inspect. I will service as needed. I have read about chamfering leading edge of shoes, and will sand them down these leading edges.
I also know about arcing shoes to drums but I believe that may be a practice rarely employed anywhere/anymore.

When the time comes to replace shoes, I will search for someone (hopefully near me) that will turn drums and arc shoes accordingly.