This same error is added to the PHP Error Log every time I do anything on the site:
PHP Notice: Undefined variable: matches in /home/xxxxx/public_html/wp-content/plugins/bulletproof-security/includes/db-security.php on line 486
These are the lines from the file:
485: // Prevents BackWPup coding mistake from displaying BPS Pro Dashboard alerts on the BackWPup Backups page
486: if ( ! preg_match( ‘/page=backwpupbackups/’, esc_html( $_SERVER[‘QUERY_STRING’], $matches ) ) ) {
I even went so far as to install BackWPup just to see if the error would stop, but the error continues with or without the BackWPup plugin.
Yes, the suggestion to do troubleshooting is all fine and well, but the error occurs whether or not BackWPup is installed. The undefined variable is in your code, not someone else’s code.