I followed FB's instruction to add a Facebook like and share plugin to your web page, the block should show like blue button and share button, but I get nothing but a blank block.
After hours of investigation and experiments, I found the block will show like and share buttons before the specified URL gets any like, after the URL gets likes, the block changes to blank. Here is the test, in the preview area of the instruction page, the blank block showed buttons after I set a non-existing URL:
Then I found that the blank block issue only happens on "standard" layout, the other layouts (box_count, button_count, button) works fine. It seems a bug of standard layout.
Changing the data-layout attribute from standard to box_count, button_count or button can solve the problem.