To get design (from other template from BeTheme) have installed in subdomain as new wp with clean BeTheme installation (last update). Have updated to last wp core and installed only suggested plugins. The option to export from Muffin Builder works fine becase all code is generated, but when try to import that content in a new page from that installation, the import option doesn´t works, I pasted code but nothing happens. Think that some plugin was problem, but deactivated all and only let active classic editor as you suggests at https://forum.muffingroup.com/betheme/discussion/43719/wordpress-5-0-gutenberg-and-betheme#latest
For now the demo content as https://themes.muffingroup.com/betheme/ is installed in our temporal website http://temp.fecobal.altercom-la.com/
If you need get access to this installation please let me know, thnks advance.