The value for the quiz setting Or all available attempts completed setting gets lost when a teacher edit/saves the activity when a student has already completed it.

1. Create a course.
2. Enrol two students.
3. Turn editing on.
4. Add a Quiz activity.
   • Grade to pass: 5
   • Attempts allowed: 1
   • Completion tracking: Show activity as complete when conditions are met
   • Student must view this activity to complete it: ticked
   • Student must receive a grade to complete this activity: ticked
   • Require passing grade: ticked
   • Or all available attempts completed: ticked
5. Save the activity and add a true/false question onto it.
6. Log in as one of the students.
7. Take the quiz and make sure you submit the correct answer. The completion for the activity should be ticked on the course contents page.
8. Log back as the teacher/admin.
9. Edit the Quiz setting and check that the "Or all available attempts completed" is ticked.
10. Save the Quiz setting, without changing anything.
11. Edit the Quiz setting again. Check the value for "Or all available attempts completed".
    Result: The setting is now unticked/disabled.