Featured image breaks embedded video

Hello!

I am using the Enlightenment Theme (https://www.onedesigns.com/themes/enlightenment) and trying to use the video shortcode from the WordPress Codex (https://codex.wordpress.org/Video_Shortcode) with a YouTube link, but having trouble when using this shortcode in a post with a featured image.

I believe have isolated this as problem because I have tried to have this work in multiple different posts and post types and tried multiple different featured images and embedded videos.

The consistent result is using [video src="https://www.youtube.com/watch?v=XeaY6AZN9S4"] with a featured image makes the video so it won't load. Using the same embed code without a featured image works every time.

I would like to have a featured image and have the WordPress Video Shortcode work... Can you help?