Doh! The plastic got stuck in the pipes! No more prints for a bit.
You might see some of the red ABS plastic stuck in this part. It's called the "Thermal Barrier" and it fits above the hot nozzles that squirt out the plastic, and below the stepper motors that feed the filament into the nozzle.
Here's a bottom's up view, with the nozzle removed, where you can see the red plastic stuck up in there :(
So, what to do? Take it all apart & soak this in an acetone bath. ABS plastic dissolves in a few hours in acetone, or at least gets soft enough to clean out that gunk easier.
Success! It took patience in taking it apart, cleaning it, reassembling it, and calibrating the sensitive leveling all over again. But, it's worth it to be back on-line & printing again!