New in version 3.0.0.
Some flavours of Linux come with a syslogd that can’t cope with the normal message format WPf2b uses; basically, they assume that the first part of the message (the tag) won’t exceed some (small) number of characters, and mangle the message if it does. This breaks the regex in the fail2ban filter and so nothing gets blocked.
functions.php will make WPf2b use
wp as the syslog tag, rather than the normal
wordpress. This buys you 7 characters which may be enough to work around the problem, but if it’s not enough you should look at WP_FAIL2BAN_HTTP_HOST or WP_FAIL2BAN_TRUNCATE_HOST too.