The issue you are facing is because you are using a very old version of the theme: 8.1.2 and the very latest version of the theme is: 8.3.4 here is the changelog: https://xstore.8theme.com/update-history/
So my suggestion to you is, please completely reset your WordPress and delete the theme and child theme from your site and Install the new theme on your site and then try to import the same demo again.
Otherwise, after completely resetting your WordPress, please let me know I will Install the theme for you on your site and Import the same demo as well.
