Hello,
The issue is that the demo content might not have been imported correctly, or some elements were imported in a different format than expected.
Please try to deactivate the third-party plugins and import the demo again.
Note that our dummy content works only on a fresh installation. If you have some content already, it will conflict with your existing posts, and most of the content will not be imported correctly.
If the issue still remains, let me know I will further check on your site and import the fresh demo on your site.
Best Regards,