Due to security reasons I’m blocking external HTTP requests on many of my sites through a setting in wp-config.php. See this article for further exploration on working security through wp-config.php. Here’s the setting:
define( 'WP_HTTP_BLOCK_EXTERNAL', true );
This measure prevents a couple of plugins – mainly premium plugins that are not available through the offical WordPress plugin repository – from fetching their updates.
This was the case as well for the popular WPML multi-language plugin.
The fix is easy – by allowing WordPress to call only certain servers. In this case it is the server d2salfytceyqoe.cloudfront.net – as detailed here in the WPML support forums. This is how it looks in the wp-config.php:
define( 'WP_ACCESSIBLE_HOSTS', 'd2salfytceyqoe.cloudfront.net' );
You probably want to add more servers here, like *.wordpress.org et al.
UPDATE NOV. 25, 2017:
define( 'WP_ACCESSIBLE_HOSTS', 'api.wp-types.com, d7j863fr5jhrr.cloudfront.net' );