I write a script for Tampermonkey to view the video, leading the mouse over the thumbnails: YouTubePreview.js
Everything works on the main page, in subscriptions and on the search page, but does not work on the video page. The sound is played and I can shake it back and forth with the mouse, but it seems like the iFrame is transparent. I still see a thumbnail image, but if I remove it, only a white empty place remains (there is no video under it).
What is the reason for this strange behavior? Maybe my player conflicts with the player on the video page?