Plugin crash when logging failed login attemtps

Running 4.5.2 with plugin version 3.01.

Logs successful logins.

Failed logins result in crash and the following items in the debug log:

[15-May-2016 08:11:26 UTC] PHP Warning: Illegal offset type in isset or empty in /var/www/html/wordpress/wp-includes/cache.php on line 725
[15-May-2016 08:11:26 UTC] PHP Warning: array_key_exists(): The first argument should be either a string or an integer in /var/www/html/wordpress/wp-includes/cache.php on line 725
[15-May-2016 08:11:26 UTC] PHP Catchable fatal error: Object of class WP_Error could not be converted to string in /var/www/html/wordpress/wp-content/plugins/wp-fail2ban/wp-fail2ban.php on line 144

https://ww.wp.xz.cn/plugins/wp-fail2ban/