Hello and thanks for your accurate description.
In mobile video backgrounds never worked and (for the moment) are not supported. That is a Visual COmposer aspect indipendent from the theme (will happen the same with every theme).

Embedded videos in mobile are for the moment fully experimental, and we are analyzing this function for mobiles right in this period, but is supported from very few devices and still is pretty buggy and not really responsing to the normal behaviors of the video.

Visual Composer doesn’t provide any support for this, also because is so rarely supported that it would make no sense in trying.

I think this will change soon, as soon as all the operative systems and mobile browsers will start to support embedded videos.

For the moment, the best solution is to also specify a background image, in the design section of the row, that will appear under the video, and in mobile will replace the video.

ADVANCED SOLUTION: for mobile, you can also add a row, and in the columns inside, go in the “Responsivity” tab, and display the row only in mobile.
Then add in the row a button to the video, so also mobile users will have an alternative way to see it.