Upon investigating, I see that you have HTTP and HTTPS for your site URLs which create redirect loop back and forth.
Then I have re-installed Pro theme, re-generated your permalink settings and then I see the following error when loading header/footer builders.
Failed to inflate gzip data SyntaxError: "JSON.parse: unexpected end of data at line 1 column 1 of the JSON data"
I suggest you to contact your hosting provider to check gzip compression settings or if you can disable any caching from your hosting control panel temporarily and test this issue further.
Also if you can switch to another PHP version, perhaps PHP v7.1.x or v5.6.x and test to see if there's any impact.
Let us know how it goes.