Hi Tikaram,
I was getting this on Facebook, Twitter and Google Plus. I checked again this morning and it is still doing it on Facebook and Twitter, but Google Plus is now picking up a thumbnail from the first YouTube video on the page. I have been testing this with my Home page.
I don’t know if this is related, but I also notice that when I make an update to a page/post I get a warning box about leaving the page and losing changes, even though I have clicked the update button several times.
Regards,
Paul