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

My new to me Toyhauler has brakes that bite hard and shudder when stopping at speeds of less than 5mph (when coming to a stop).

What is the usual culprit for this issue?

Is this a common issue for older brakes?

The trailer sat for the last two years.
Brakes are Dexter and are on 6000# Dexter axles (8 lug).

I'm assuming all parts are original since original owner said he never serviced brakes over the years as they always worked fine.

Thanks