I've ran hundreds of pounds of various mfrs.' pellets though my 570 and have never had that occur. They have made a design change on the paddle wheel arrangement. Rotated it 90 degrees on the newer models. Which way does yours sit? Are the "fins" of the paddle parallel with the width? Mine is that way and works fine but there must have been some reason they now have the fins running parallel with the front to back direction.
Like the other posts mentioned, probably just moisture. As long as you keep your pellets in sealed containers so they don't absorb humidity and keep the pellet hopper high & dry, you shouldn't have any problems.
American BBQ Systems model All Star, CS-570 & TG-300 pellet grills, Broilmaster P3, and lastly, Superfast Red Thermapen