Why doesn't my iframe pause when I close a Modal popup?

This has to do with the iframe settings.

Our developers have built our tools to close an iframe, if possible. However, when a video is in an iframe, we have no way of knowing what is going on inside of that iframe. YouTube provides a way that we can tell the video to stop playing, so that's why Youtube videos are fine. That is the only integration platform of which we are aware that provides a way to do that. 

If your video is added inside a DesignPLUS accordion or tab, we would recommend adding a note beneath the video explaining to pause it, as the video will continue playing after closing the accordion or tab.