Because the the propagation of files in the
http://cdn.mathjax.org/mathjax/latest directory can take several hours, it is possible that your users will get some files from v2.1 and some from v2.2 during the propagation phase. They can also have v2.1 versions in their browser caches, and so get a mix of v2.1 and v2.2 that way. That can lead to math processing errors, or math not being processed at all. So you might want to switch to
http://cdn.mathjax.org/mathjax/2.2-latest/MathJax.js temporarily, since it will not be in cache, and will not have old version on the CDN edge servers. Once the CDN copy of mathjax/latest has stabilized (should be complete within 24 hours), you can switch back.