Hello,
1) Sorry, but you still did not solve the problem with Customizer and the default theme. We can’t proceed with checking our theme issue if customizer does not work even with the default theme on your site. Seems your hosting provider have some limits for WP options. Contact hosting support and solve the problem https://gyazo.com/bdb2e22363fe4e0de128c353a60fdeef . Reply back only after that.
2) We are able to connect to your SFTP but could you tell me in what folder your WP installation is located? Because we checked a few of them and did not find.
Regards