Oh, no students in the course. "now" was a typo. I tried to send a file with images, but it was too big. After hours of trial and error, the rubric is now showing up. But I don't know why. Where is Moodle putting it? How long does it take, after saving it to become ready, does it take to show up?
I have been through several rounds of trial and error. See last page. Something finally worked.
Finally, it showed up.