Hey
Thanks for reaching out to us!
Strange on your site. It looks like the ajax load of that first link works fine. Go to the month view and click the next month links until you get to “/2015-12” and you’ll see that the page loads. If you then reload the page you get a 404.
I tested this on my local install and wasn’t able to replicate. As an initial step, have you tried following the Testing for Conflicts procedures to ensure there isn’t a conflict at play currently?
Let me know if this helps.
Thanks!