I switched the default “Twenty Sixteen” theme and received the same error. The error is unknown URL.
The URL I am trying to input is https://www.youtube.com/embed/-CSq9NoRyTU?rel=0&modestbranding=1
This is https://www.youtube.com/embed/-CSq9NoRyTU with ?rel=0 and &modestbranding=1 added
I put https://www.youtube.com/embed/-CSq9NoRyTU?rel=0&modestbranding=1 directly into the browser and it works as it should. It just will not work when I try to add it into the gallery.
