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Its not really an intrinsic problem with Rockys alone, more to do with the diameter of the throat into the grinding chamber. As the throat diameter decreases, it lends itself to beans "bridging" across and causing a log-jam of beans from the hopper. One way to reduce the likelihood is to only fill the hopper with enough beans for immediate use. This isnt a bad idea because it ensures your beans are kept fresher for longer if you keep them stored in the 1-Way Valve bag they come in.
If they still tend to "hang up" then maybe the beans are a little oily and sticky. They can be dislodged easy enough though, I used to use the handle of the coffee scoop that came with my Rocky as it is flat and flexible enough to feed down into the top of the grinder throat and dislodge the bridged beans. Only do this with the grinder turned off of course. Hope this helps... :)