Did you add the Results slide manually? If you have real quiz slides, not the Knowledge slides, the results slide is added automatically. That is the reason for my first question. Knowledge check slides are automatically reset when returning to the slide. You may have a look at this blog post, where I compared both types of slides.
https://blog.lilybiri.com/knowledge-check-slides-tips
Something you need to check as well is the Advanced Interaction panel (F9). If you have scored quiz slides the total Quiz score appearing on top of that panel should show a significant number, not zero. Since you get a Passed score it could mean that the learner has 80% of the total score, which is also zero if the total score is zero. This could happen when you took out the score for each quiz slide, which is less probable IMO. Complete description of that panel can be found in:
https://blog.lilybiri.com/advanced-interaction-panel-q-and-a
From my experiences in this forum and elsewhare I realized that this panel is unknown to a lot of Captivate developers and that is a real pity.