I came home to find two things
1. Burned electrical smell in the house
2. Dishwasher had failed to drain

I cannot tell for sure if the two are connected, but it seems likely.

The filters were not clogged, and the drain impeller does not appear to be clogged. I find the impeller does not spin freely - it resists then moves in jerks. Kind of like turning a piston-driven shaft if you know what I mean.

I tried using the posted online manual to ohm-out the drain motor from the front panel, but the schematic for the SHU 33 does not appear to match mine (SHU33A06/22).

Suggestions?

Well that was interesting.

Yesterday it would run through a cycle like normal until it needed to drain, then made switching noises like it was trying to do something but could not. Eventually it appeared to be done (based on the lights) but the tub was full of water. I removed and cleaned all filters, which were not bad. Removed the pump cover and checked the impeller was not obstructed. Checked that the drain hose was not plugged.
Today, to answery your query precisely, I ran it through a cycle... and it worked fine. Running another cycle now, so we'll see.

Possible a foreign object fluctuating in the drain line.

Gene.