There is an Opencart 18.104.22.168 issue because base href tag is not properly setup when using SSL and static assets are loaded with the wrong path. To fix this, edit catalog/controller/common/header.php and replace
$server = $this->config->get('config_ssl');
$server = str_replace('http:', 'https:', $this->config->get('config_url'));
After you make this change, refresh Opencart modifications, clear vqmod’s cache (if you have vqmod installed) and your issue should be solved after.