I am having the same problem and am Freaking out!! It dissapeared on my right before I presented a new website to a client and really made me look bad… Any clue what happened??
@robanna
As a quick fix, you could just manual add the shortcode to a text widget and your files will show up again!
Ah, yes. I added it to the theme. I like your workaround better.
My widgets also disappeared, both from the sidebars they had been placed in and the list of available widgets. (4.3)