What version of Moodle are you running? What browser are they using? If you have 3.7 or lower and they use Chrome 80 or higher or Edge (past year?), there is a 'security' feature that prevents postbacks (is that the right word? I haven't had coffee yet and am not very techie) that can interfere with score reporting. When my site was experiencing this, I couldn't duplicate it but a lot of users had the problem. Upgrading helped a lot.
SCORM
SCORM & End of Module quizzes
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