Hi Emma, specific to this quiz only. Even if I log in as the instructor I cannot see results or a report from the quiz in question. I've compared locally assigned roles and permissions for the trouble-child quiz with one that is working, and everything is set the same. I'm pretty stumped.
I have even tried exporting the grades to an excel doc, backed up the quiz with user information and grade history and tried restoring it into a sandbox course, etc. all without any luck.