I saw the same thing the other night, while trying to embed a one liner snippet from The Planet of the Apes. Probably would have added some sense to my nonsense lol. I just figured it was that regional code thing acting up on YTs end. Like maybe if it's music or film clips might be more likely, but I've seen that empty playback box with the snafu code too. Like if it won't pop up in the preview display, but seems to work fine for other YT videos, so hard to know.