How to fix error Uncaught ReferenceError: mod_pagespeed_xxxxx is not defined which you can see in console log, and if you take a look in source code of your page, you can see that something went wrong with loading combined JS files. The problem can be easily fixed, and it is caused by apache mode_pagespeeed.
Fastest fix is to flush the caches. How to do that? Well, via your terminal go to:
Fastest fix is to flush the caches. How to do that? Well, via your terminal go to:
cd /var/mod_pagespeed/cache/
and then type
touch cache.flush
and that is it.
More about this problem you can read here:
https://groups.google.com/forum/#!topic/mod-pagespeed-discuss/28c3mI0c1HA