Thanks for asking.
I checked the your licence manager page and in that I can see a dev url, I believe you are developing the website over there. Upon checking the website I see that you are using X Theme version 6.0.4 and Cornerstone version 3.1.3. You are using fairly latest version of Cornerstone (we now have Cornerstone version 3.1.5), however X Theme you have on the website is incompatible with the version of Cornerstone that's on the website. And that might be the reason why you are not able to import the demo contents.
In that regards, I suggest you to please update X Theme to the latest version. Also it's a good idea to update Cornerstone also.
I am sharing website URL and screenshot of the test in secure note.