Video problem – If size of browserwindow < 768 px no video is showing

Dear all,

I am creating a page for a customer.
He decided to go with an animated background in form of a youtube video.

I have activated the feature in WPBakery (use animated video background) entered the link to the youtube video and set Parallax to no.

Now the problem: When I visit the webpage on my desktop (all browsers tested), everything works fine until I lower the width of the browser window below 768 px, then the video vanishes. This is consistent with the behavior that the video is not showing up at all on my iPhone 8 in portrait mode.

Help is highly appreciated!

All the best,
werbefreiheit