The configuration looks good to me so it's most likely due to Mathjax's CDN having issues. You can write them directly about it. I've done so in the past and they were very helpful. The only thing to possibly change I can think of is to move down the Mathjax code from the very top of the header. Downloading javascript files stop the loading of other elements until it's complete so if there is a hangup then it could stop this site from loading properly. What I do is place all the code in the "headinclude_bottom" and we rarely get these issues. It's worth a shot. Lastly, Chrome seems to have the most problems with Mathjax, so much so that I just don't even try.
