Our WordPress 3.9 install was working just fine before using previous version of Feed JSON Plugin. Recently, we updated the plug-in to v1.0.9. As a result, several users reporting problems with the blog, such that no posts were being displayed. Chrome Developer Tools Console showed the following errors:
Uncaught ReferenceError: jQuery is not defined jquery.reveal.js:159
Uncaught SyntaxError: Unexpected token < blog.brackets.io/feed/json?callback=jsonp1:1
We were able to restore our site by deactivating and deleting the Feed JSON Plugin, and then installing and activating v1.0.8 instead. Everything seems to be working fine now.
Was there something else that we should have done to upgrade the Feed JSON configuration?