title: White image as Youtube video preview
body: <p>I am embedding Youtube videos in a web site but sometimes (it is not a deterministic error, sometimes everything works fine, sometimes not) instead of the youtube preview image, only a white square is rendered.
  If I inspect the element, I can see that actually there is a tag IMG with the correct SRC attribute, and if I navigate this URL I get the correct image.</p>
  
  <p>Is there any reason why I get the white square in the web site?</p>
  
  <p>Thanks,
  Stefano</p>