Hi, I tested your shortcode and this is the message I receive when trying to play the video.
Because of its privacy settings, this video cannot be played here.
So, my guess is that private or secured videos will not display the thumbnail. However if you test a non secured video, the thumbnail will show up. I have also tested the shortcode with a none secured video ID and the thumbnail shows up.
This reply was modified 1 year, 5 months ago by mbrsolution.