I just updated Jetpack and the theme, and the infinite scroll doesn't work anymore.
I have tracked the console, and the XHR does receive the content of the posts to add but somehow it isn't displaying them.
My blog is: http://jorjon.com/blog/
I have no custom modification whatsoever.
Uncaught SyntaxError: Unexpected token < jquery.js:2 v.extend.parseJSON jquery.js:2 (anonymous function) infinity.js:208 l jquery.js:2 c.fireWith jquery.js:2 T jquery.js:2 r
Update 2: This is what is being returned by the XHR, supposedly there is an unexpected token there, but I can't find anything. The JSON at the last line, as Jared mentioned, is Valid. http://pastebin.com/ZUD2xqun