KitchenAid Dishwasher Drain Pump runs intermittently

KitchenAid KDFE104DSS5 stopped draining recently and I took the following steps:

A. Blockage in Drain Hose:

1) I used the "Cancel/Drain" option successfully once and then this option stopped working too.

2) I found the drain hose clogged at the end connecting to the garbage disposal (there is no air gap). I cleaned the guck and tested it end to end for clear movement of water.

3) When I ran the Dishwasher, it still wouldn't drain (and pressing the "Cancel/Drain" button produced a soft vibration hum, likely due to the drain pump motor trying to run?)

B. Drain Pump Running Intermittently:

I pulled out the dishwater and extracted the drain pump out (Part #W10724439). I fond nothing impeding the movement of the impeller.

1) While holding the drain pump, when I pressed the "Cancel/Drain" button, the impeller worked for about 15 sec and stopped. However, I could feel the vibration from the motor unit. When I nudged the impeller wings, it would start running again.

I tested it a few times using the "Cancel/Drain" button and found the behavior inconsistent. Sometimes, it would run continuously and sometimes, stop (and start running again if I nudged it).

2) I unplugged the drain pump from the dishwasher and pried open the back plate of the impeller and found a very thin dry residue (looked like soap scum) around the circumference. I cleaned it (attached pic)

3) I then hooked it up directly to a 120V source. Every time I switch on the power, it runs continuously without any interruption.

I am now stuck and unsure what to look for next. Would appreciate some pointers.