Wordpress blank screen after uninstall plugin/ deleting post

Using wordpress, but after some time use, when i deactivate/ativate plugin
or delete post, then white screen with text "Error is getting display".

After enabling the Debug, getting below message Please help

for constructors WP_Widget is since version 4.3.0 of date! Use instead __construct () , in /var/www/vhosts/briefmich.de/httpdocs/wp-includes/functions.php on line 3457

Notice: The used method for constructors WP_Widget is since version 4.3.0 of date! Use instead __construct () , in /var/www/vhosts/briefmich.de/httpdocs/wp-includes/functions.php on line 3457

Notice: The used method for constructors WP_Widget is since version 4.3.0 of date! Use instead __construct () , in /var/www/vhosts/briefmich.de/httpdocs/wp-includes/functions.php on line 3457

Notice: The used method for constructors WP_Widget is since version 4.3.0 of date! Use instead __construct () , in /var/www/vhosts/briefmich.de/httpdocs/wp-includes/functions.php on line 3457

Notice: The used method for constructors WP_Widget is since version 4.3.0 of date! Use instead __construct () , in /var/www/vhosts/briefmich.de/httpdocs/wp- includes/functions.php on line 3457

Notice: The used method for constructors WP_Widget is since version 4.3.0 of date! Use instead __construct () , in /var/www/vhosts/briefmich.de/httpdocs/wp- includes/functions.php on line 3457

Please help me out.

via Chebli Mohamed