Hello @Carter41
Thank you for contacting the Instructure Community. We're sorry to hear you've been experiencing issues with quiz questions. The questions for multiple correct answers vary depending on whether or not you are using classic or new. For classic quizzes, users often have trouble with this question type as it is an all-or-none style in regards to the points administered and any messages also displayed. Did they select some correct answers? Then it will show that - but correct answers that were not chosen would count against them. It should be displaying that they missed the points/questions however and not just blank. It may be how you set this question up.
If you were using New Quizzes, there is a bit more flexibility in how you want the points calculated:
How do I create a Multiple Answer question in New ... - Instructure Community
If none of this is helpful, then you may want to contact Canvas Support directly to pinpoint the source of the issue and provide a resolution:
How do I contact Canvas Support? - Instructure Community