The cause remains a mystery. The solution was to remove the cartridges and put them back in. We suffer frequent transient power outages. I had to remove and reinstall several times.
I have since gone through several sets. The problem has not reoccured. I do not think the problem lies in the printer but something in that set of ink cartridges.
The diagnostics could offer more 'in the weeds' detail for those of us who would welcome it. Or a big reset button - a simple reset likely would have solved the problem.