Server error on login and logout

I’m getting the following server error whenever I log in or out of my site after upgrading to latest version:

mod_hive matched URI http://www.mywebsite.com/wp-login.php (/home/username/public_html/mywebsite.com/wp-login.php) with match 2, referer: http://www.mywebsite.com/wp-login.php?itsec-hb-token=backend

Web host (siteground) suggest it may be a permissions error or perhaps a PHP version issue (PHP is on 5.6.30).

Any thoughts on what I can check/look for?