"A conflict on the front end of your site has prevented the preview from loading." in general is a generalized error message that can mean one of many things. Please make sure to read the following thoroughly and follow all steps outlined.
The message can be caused by the following:
Incorrect setup of SSL. If you have an SSL certificate on your site. You should have the WordPress Site URL and Address URL settings set to HTTPS if you are loading the builder via HTTPS. This can be checked via your wp-admin > general > settings. If you aren't using SSL you can ignore this step.
Caching. If you have a caching plugin activated or any form of server side caching please disable it to test for any possible conflicts. If you have server side caching or aren't sure if you do, your host should be able to advise of this and disable it for testing purposes on your account.
Cloudflare. If you are using Cloudflare please disable this for testing purposes. Cloudflare by default enables an auto minfication function to compress the JS and CSS files of the theme. As the theme already serves minified files, re-minifying said files only causes to break the entire site.
Custom code syntax error. If you have a child theme, please enable the child theme and check if the issue still exists. If you have entered any custom JS or CSS into their respective editors. Please review the code for any syntax errors. A mis-placed semi-colon or a missing bracket will cause the issue you're seeing.
If you could please try the above and if you still have the issue we'd be more than happy to assist.