Course Freezing

I'm having major issues with a course, up until the past few days it's been fine (it's been in development for about a month now), but now the audio and visuals are freezing but the scrubber bar keeps going. Once it does that eventually the whole course starts to buffer and become completely unresponsive.

The course is made up mostly of videos, there are 10 videos, a hub, one click to reveal slide, and a multiple choice activity. Overall the interactivity isn't complicated and the course isn't long so it's pretty puzzling. Several other members of my development team have looked into it and we can't find a solution, which is leading us to think it's a Storyline issue.

Here are the things we've tried:

• compressing all of the videos again
• publishing in SCORM 2004
• saving a new version of the Storyline file
• publishing from a different computer
• inputting all of the video files again by placing them on the timeline again rather than using the replace option
• swapping the .mp4 videos for .mov versions
• testing it on our LMS as opposed to SCORM Cloud
• publishing it in older versions of Storyline (Nov 30th, Nov 2nd, Sept 28, and Aug 31st)
• testing it with a simpler hub slide
• testing it with only 4 slides and 1 being simplified
• testing in most current Edge, Firefox, and Chrome browsers

Any suggestions of things to try? We're really scratching our heads with this one and it's supposed to be delivered to a client soon so we're trying to figure it out fairly quickly.