I have the same issues. I do have Disconnect running, which blocks about 30-40 third-party requests made from your site. It looks like errors from mixpanel are breaking the rest of your app.

I do allow same-party interaction and cookies. (i.e., anything from montagebook will work.)

You may want to set your third-party analytics services to be asynchronous, so they aren't a single point of failure for your entire application.