Sorry about my slow response.
I took a video of the machine jamming during a calibration print. It printed fine for about 13 minutes, then slowly started having trouble releasing off the pdms. It's a long video, and as I don't really know much about video editing / compressing. https://photos.smugmug.com/photos/i-sQT ... HT-640.mp4
I sent that video to the good folks at B9 technical support. The consensus was that the printer's mother board was bad. I purchased and installed a new one.
But now the printer wouldn't print at all. Of course the board had to be bad. B9 folks suggested I replace the usb and hdmi cables; reluctantly, I did. And it fixed the problem.
Could the cables have been the problem all along? I don't know. I don't believe in coincidences, though.
Regardless, the printer is working. I'm back in business. I don't have to beg friendly competitors for model printing. And I'm happy.
And that's all there is to it.
My thanks to the folks at B9 Technical Support