The demo content installation problem is usually because of the hosting service provider restrictions. It might cause by several reasons that I will list below:
1) Make sure that you have the PHP maximum execution time of 300 or above. For more information:
2) Make sure that you increase the PHP memory limit. For more information:
3) Ensure my site can reach this domain: community.theme.co
4) Ensure cURL is working, and allow_url_fopen is enabled.
5) Ensure PHP is configured with the latest CA Root Certificates.
For all the point above you need to contact your hosting service provider to follow up.
As a final resort, you can move the WordPress installation to your local machine and follow with the demo import process and then move it back to the server.
Needless to say that it is not recommended that you import demo content into an existing website as it will override many options and you might miss configurations. Try the demo import process on a clean install of the theme and WordPress.