Thank you for your question!
The issue with a video can occur if there is a "broken" frame within the video. So, to solve this issue, you need to reconvert the video file and re-insert it into your course.
To re-convert the video, please open iSpring Cam Pro -> New Project -> Add a video -> Publish -> My computer. Then the video in mp4 format will be created. Please add this new version of a video to your course.
Hope this helps!