your toilet paper can get as hard as a rock, and block the suction in the tank.
its not the pump or the shredder.
pull the bottom hose off, and check, be prepared for the brew to leak, so dilute it full with clean water and blue chemicals.
You could disconnect the hose at the bottom of the pump, and poke the clog with a coat hanger..... watch out for water fountains...
poop tank on its side