Please can you copy and paste the exact error message you are seeing.
It might be worth setting Debugging to DEVELOPER level during the upgrade. That link tells you how to change debugging even if you cannot get to the admin screens.
(Also, making backups should not be a matter of luck )
The quiz reports do not yet use enrolments property (MDL-27072).
What they do at the moment is list all users who have the mod/quiz:attempt capability in your course.
If all users are showing up, that suggests that there is something weird with your Roles set-up. Not all uses should have that capability in your course.
I had an idea which is, we could have a display of the right answer for teachers that appears in a different place / style to the right answer that is shown to sutudents depending on the review options. I am not sure if that is a good or bad idea.
It is buried in the paragraph of text after the query:
does not quite work in MySQL. You need to change 'CAST(st.event AS varchar)' to 'st.event' in the middle
We just need to look at the data from one or two problem attempt ids.