It's called a broom stick!This happens where the pellets feeding into the auger create a sink hole or vortex in the hopper. I simply move the pellets around throughout the cook to make sure that the auger is being fed. I'm sure some of the geeks on here have a fix, but I haven't seen a reliable one yet.
I think I remember someone talking about a vibrating mechanism that would prevent this. Ok, I know what some of you are thinking already...