OK I think we figured out what happened, and it actually is extremely similar to the case that I mentioned in my previous reply to @tdelillo . Here is what the instructor said:
"I think what happened is that the student started the exam on her computer, a Mac. When Excel froze on that computer, she opened needed Excel files from a CLC computer, which required going into the exam quiz to access file links. She submitted from the CLC computer, but Canvas did not record that, even though it was scored - a 90 before questions that I needed to manually grade. The score of 90 matches my sense of Danielle's understanding of the material.
Students have opened exams in multiple machines before, and I was nervous the first time, but it worked fine - until this case! Perhaps I should have a separate module of files for exams, so an exam quiz is open only for answering questions."
Combined with the previous example (see reply above), it sounds like (either sometimes or always, we cannot verify at this point) Canvas takes the first time ever opening the quiz as THE attempt to keep the score of, although it would make the most sense (to me and to others I hope!) if the session actually submitted, no matter if it was the first time the quiz was opened, should be regarded as the attempt to keep. If someone could get the attention of Canvas to fix this flaw, it would be great! As you can see it happens more than once.
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