Joost, this just happened to me too! I was pulling my hair out trying to figure out why the Review link was greyed out for students with a closing date override, even though I had it enabled in the quiz settings. If the ticket Mary posted isn't related, consider making a new one and posting it here so I can give it my vote! We need a way to 'lock' the quiz down for some users but NOT remove their ability to review their old attempt.
Quiz
User / Group overrides and release of Quiz grades
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