@marymwillis
Do the student names show up in SpeedGrader when you try to change between students or are some of them missing? You showed a picture of the test student, not an actual student.
If the names aren't there at all, as opposed to the name being there but the quiz just not loading, then it is may be a missing submission record. Part of the symptoms are the inability for students to see the assignment and missing names in SpeedGrader.
If the names are there but the quiz just doesn't show up even though they've taken it, then it's something else.
Canvas "fixed" the issue (it was related to content that was imported in December / early January) so that new imports don't have the issue. But they didn't fix the issue for those assignments created during that time period. This is the second thing I've read today that sounds like this issue.