Course loading error at the end of a quiz

Hi all,

I'm experiencing an issue with a course, we can navigate through the course fine and there is a 10 question quiz at the end. When a learner reaches the final question and clicks Submit the course freezes with a continual loading icon.

It is being recognised as complete by the LMS itself (even if we failed the quiz), but we have to completely close the course to come out of it, it doesn't migrate to the Results slide per the trigger set-up. 

I have tested it through the SL preview and within SCORM cloud, we've used different browsers. I've rebuilt the quiz entirely, the issue persists. I am able to replicate the issue every time, there was one instance last week where I tested the problem file in SCORM cloud and it work fine (once). 

Any advice, would be much appreciated.

Cheers,

Kaanon