Reasons why bottom auger might be stopping?

Check the set screw on the auger motor to auger connection....if it's loose, the auger motor might be slipping.

This is from Englander web site under "Troubleshooting":

"Lower auger not turning. If the lower auger is not turning the following should be checked;

1. Is the auger physically jammed? Foreign objects such as wood chips or other objects that may have somehow gotten into the pellets.
2. Is the motor getting power? If the motor is getting power it will get fairly hot quickly. If the motor is getting power but is not running and the auger is not jammed, the motor is bad. If the motor is not getting power, either the motor's wires or the control board are bad.
Another possibility is if the electric motor is running but the auger is not turning, this could be a loose setscrew holding the motor to the auger, or a stripped gear in the gearbox. A stripped gear would mean the auger motor must be replaced."

Also go through this thread and the others referenced within: https://www.hearth.com/econtent/index.php/forums/viewthread/34017/

Crud in your vacuum line?

Bad hooper seal?

swap the two motors its possible the lower motor may be getting weak, the two motorsa are identical, by swapping you take the weakened motor to the top where it only runs about 10% of the time and put the fresher motor on the bottom

Just wonderin how old this stove is. I'd also like to know if Mikes advice worked (swapping the motors) I get this call from folks with the 25 once in a while. Then I can help folks instead of just passing out Mikes personal email address.