Using Apache 2.4.18 and PHP 7.0.8-0ubuntu0.16.04.2 I get these apache errors where the rendering of the webpage leads to a bad gateway problem
[:error] [pid 9090] PHP Waing: Declaration of FDX_Widget_search::form() should be compatible with WP_Widget::form($instance) in wordpress/wp-content/plugins/wp-twitter/modules/class-p2.php on line 0