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The control box is as good a guess as any. However I suspect a problem with the pellets being used, have you tried several other brands of pellets, and are you making sure they are fresh dry. Older pellets absorb moisture, swell up, and then do not feed well.
Let me know about all that, we can go from there.
It is possible the pellet mfgr has changed the manufacturing process or that the latest batch of pellets had been stored improperly or too long and now have a higher moisture content, and slightly larger diameter.. or that the wood mix in that batch of pellets has changed.
For a test only, and in order to educate ourselves on that possibility, lets just try another brand of pellets and see if it is actually a factor, or not. That will be a lot cheaper than changing components.
Let me know if that sounds like a good idea to you or not... we can go from there without a time limit.