Hello, @sk,
Actually, It looks like you imported the demo with one-page builder and tried to edit with another page builder which destroyed your site, and we do not recommend using multiple page builders on the same site at the same time as this caused unexpected issues.
So please reset your WordPress and start from scratch. Please install only 1-page builder whether “WP Bakery or Elementor” and then import the demo with it. I am sure you will not face this issue anymore. But if yes then please share your site credentials in the private content area so that I will check and dig more in deep to find the cause of it and fix it.
Regards 8Themes Team.