Videos cut off

Hi

I'm using the latest version of captivate on a project that involves a lot of video (mp4). All works perfectly in Captivate preview and when I publish (SCORM) to our LMS (Moodle) and preview there. But when I access it as a user the videos and audio files randomly cut off either at the start or at the end. I've tried adding a pause on exit but it makes no difference. 

I can see others have had similar issues over the years but cannot find a definitive solution anywhere. 

Can anyone help please?