thumbnail not showing on mobile

Hello, I need some help to see why I cant see the thumbnail or if it’s not possible to see it. I had check on different devices (android and iOS).

I can see perfectly well the thumbnail on my desktop version of the page, but on mobile I only see a black screen with the YouTube logo and the play button, it works perfect though.

Is there something I need to check for? Do I need a plugin for that?
Thanks.