Correct your php code.

Apache2 2.4.25 working in mpm prefork mode on Debian 9.8.0 PHP 7.2.16-1+0~20190307202415.17+stretch~1.gbpa7be82 (cli) (built: Mar 7 2019 20:24:15) ( NTS ) Copyright (c) 1997-2018 The PHP Group Zend Engine v3.2.0, Copyright (c) 1998-2018 Zend Technologies with Zend OPcache v7.2.16-1+0~20190307202415.17+stretch~1.gbpa7be82, Copyright (c) 1999-2018, by Zend Technologies My Apache2 access.log and errors.log show this. PHP Warning: Use of undefined constant DOING_AJAX – assumed ‘DOING_AJAX’ (this will throw an Error in a future version of PHP) in /var/www/html/example.com/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php on line 170, referer: https://example.com/wp-admin/index.php [Mon Mar 25 17:39:44.476486 2019] [php7:warn] [pid 2284] [client 176.XXX.XXX.XX:31255] PHP Warning: getimagesize(): Filename cannot be empty in /var/www/html/example.com/public_html/wp -content/plugins/protect-wp-admin/pwa-class.php on line 271, referer: https://example.com/wp-admin/index.php [Mon Mar 25 17:46:08.347080 2019] [php7:warn] [pid 2274] [client 176.XXX.XXX.XX:31274] PHP Warning: getimagesize(): Filename cannot be empty in /var/www/html/example.com/public_html/wp -content/plugins/protect-wp-admin/pwa-class.php on line 271 This topic was modified 7 years, 2 months ago by Sysadmin . I am getting the same thing when going to my /wp-admn page: Warning: Use of undefined constant DOING_AJAX – assumed ‘DOING_AJAX’ (this will throw an Error in a future version of PHP) in /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php on line 170 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 1251 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 1254 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-login.php on line 453 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-login.php on line 468 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-admin/includes/misc.php on line 1196 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 957 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 958 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 959 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 960 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 961 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 962 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 965 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 966 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 969 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 970 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 971 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 972 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 975 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 976 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 977 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 978 Warning: Cannot modify header information – headers already sent by (output started at /home/treeof51/public_html/wp-content/plugins/protect-wp-admin/pwa-class.php:170) in /home/treeof51/public_html/wp-includes/pluggable.php on line 981 @palanthir Same Issue for me and broke entire webshop of a client. Seems that more have this problem: https://wordpress.org/support/topic/php-warning-getimagesize-filename-cannot-be-empty/ I suggest to get an other plugin for protecting you admin, Because the developer is not responding! This fixed the issue on my site: https://wordpress.org/support/topic/php-notice-131/