What version of Moodle is this? Are there any warnings shown on Site administration ▸ Notifications?
Can you share any screenshots of what the learner sees when completing the quiz and what's being seen in course administration? (Remove or hide any information that shouldn't be shared on the Internet).
Presumably this issue is with the Quiz activity? This has a dedicated forum where the quiz experts are, so you may want to re-post your question there, along with the above information.