On my MM3 mill the non-driven roller will get stuck now and then. It's inconsistent so I normally drop a few grains in before pouring in the whole batch (as someone mentioned earlier). I think whatever is stopping it get caught between the dead roller and the bottom roller, sort of like something ends up on the wrong side of the roller for some reason. When it gets stuck, I have to turn the lower roller backwards by hand and it generally works fine from that point on.
My old BC worked great until the teeth got too smooth. Sent it back to be reconditioned and it worked for half as long as the first time.
Paul