functions.php does not have a php close tag ?>
I received a 404 warning about a resource not being found. It was the result of:
wp_enqueue_style( 'roboto-slab', '://fonts.googleapis.com/css?family=Roboto+Slab:400,700,300&subset=latin,cyrillic', array(), null );
"/fonts.googleapis.com/css?fam...etc" was being appended to my domain name, so it was looking for "likefilthyrags.com/fonts.googleapis.com/css?fam...etc" Adding the php close tag to the end of the document resolved it.