X-Theme and BeTheme not working together

Because BeTheme is a Paid Theme, I’m not able to test it on my Test Systems to try and re-create your problem.

But, running Firebug (browser Firefox debug tool) says that https://www.springleap.com/blog/ is dynamically going after https://www.springleap.com/blog/undefined/ which gives a 404 Page Not Found. Why that is, I do not know.

This is only a guess, but the first thing I suggest checking is that your Theme Selection setting in my plugin is a URL Prefix, not just a URL, for https://www.springleap.com/blog/

Please let me know if that solves it or not. I can explore some other ideas, if not.