As of version 0.11.1
work around:
$ sudo cat /etc/fail2ban/jail.local
[sshd]
+ backend=systemd # <= add this
enabled = true
# To use more aggressive sshd modes set filter parameter "mode" in jail.local
# normal (default), ddos, extra or aggressive (combines all).
# See "tests/files/logs/sshd" or "filter.d/sshd.conf" for usage example and details.
backend=systemd
enabled = true
mode = normal
port = ssh
logpath = %(sshd_log)s
#backend = %(sshd_backend)s <- commented