Rise quiz not letting users move forward

Hello!

I have several rise courses that have a quiz that must be passed before moving to a final exit lesson.  For the most part, learners are able to complete the courses without issue, but there are several cases where they will get to the end of the quiz and won't be able to see their results  and can't retry or move forward. 

These are fairly large courses.  They have storyline blocks as well as several gifs. Users have also mentioned that the storyline blocks freeze or get visually warped.

We have instructed users to clear their cache and cookies and this hasn't fixed the issue.

This is not a consistent issue, most people are able to move forward just fine but others are completely stuck and we have to mark them complete manually in cornerstone.  

Any thoughts or suggestions on this issue are appreciated.

Thank you!

Leah