Sorry for the late reply. I´ve been checking all again but it still happens. As i see in your video what u click is the button “View” in the “posts list ” page. Up to here, all is fine as you saw. To see what it´s happening to me you have to be inside of the Post Page, write in the classic editor and then click “Preview Page” or as it says in spanish “Vista previa”.
Once you have clicked and a new page opens with the preview of the content, you go back to the edition page and “magic”, the post is gone! :-S