Published Storyline file won't move from one slide to another with a video on it

Having an issue when publishing a course in the program Pelesys. 

Whenever I click "preview", the Storyline file will begin, but when I click next (the next slide has a video on it), i get three loading dots and it will not move to the next slide.

This only happened recently and was a previous issue before, but we thought it was resolved. But it seems to be happening again.

Is there an easy solution to this problem?