drive motor

Most gear reduction motor assemblies are hard to turn by hand. If you state what stove or put in signature others can more readily help.

I would try the motor out of the stove and hook it up to power with a power cord to rule out the auger jam.

It looks like it is driven with a spring clip like mine and my dealer said they have sold a few replacment clips when i bought mine. Sounds like it can shear in a jam situation

Need to cut the female off a cheap extension cord and crimp on a couple of 1/4" female spade connectors to test with 120v, just plug them onto the motors spade connectors and plug the cord into the wall or power outlet for direct power to the motor.

Yes ... old lamp cord would work.
You can also pull the motor of the gear assembly. to see if the motor itself is free. If you have the motor/drive assembly off the auger ... does the auger move freely? It has a bearing set that could conceivably seize up.

Taking the motor off the gearbox, still doesn't test the motor itself.

Does your unit have a diagnostics mode, where you can run each motor independently. That might be safer than messing with the cord (although that's pretty easy to do as well.)

You might but it is the price of heat JK... just realize the two new spade plugs you add on the ends are 120v hot anytime the cord is plugged in so attach to the motor first then the wall outlet, remove from the wall outlet before handling the spade connectors /

You can briefly test the motor on the extension cord while installed and hooked to the auger as a final test.

Length of pellets should hasve no impact on the auger. Shaded pole drives make miniscule power but when you take 1800 rpm and reuce it to 1 rpm through triple compound reduction, your optput shaft is makinging some serious torque, more than enough to crush lowly wood pellets. I believe what occured was you got something foreign in the pellets, maybe a metal part from the pellet making process. That would jam an auger.

Why, when burning corn, you want magnetically cleaned corn. Things like nuts and bolts often wind up in shelled corn plus magnetically cleaned shelled corn keeps down 'hardware disease' in cattle.