This isn't your quiz. It IS the course completion settings. I don't know why but sometimes the grade condition doesn't check. It just prevents people from ever getting credit.
One thing that sometimes helps: Check your Grades. If at the top of the screen it gives you a message that says, "Note: The aggregation method "Sum of grades" has been changed to "Natural" as
part of a site upgrade. Since "Sum of grades" was previously used in
this course, it is recommended that you review this change in the
gradebook.", you need to click okay. Sometimes that will trigger the grade condition to actually function (not immediately, but on the sync cycle, you might have to reset completion, too). Of course this means sometimes it won't.
My general solution is to never use grade condition. You've set a grade to pass on the quiz (green check), so it won't give them credit without passing. The grade condition is just one more thing Moodle has to do to complete the course. Try removing it and see what happens.