RPC helper segfault - Ubuntu 18.04LTS

I created a very simple RPC helper configuration as described in
http://conntrack-tools.netfilter.org/manual.html

After starting conntrackd, the ct_helper.so causes a segmentation fault as soon as a packet hits the -j CT target in iptables.
conntrackd crashes ungracefully with lock files preventing restart.

conntrackd config:
# Default debian config. Please, take a look at conntrackd.conf(5)

General {
 HashSize 8192
 HashLimit 65535

 Syslog on

 LockFile /var/lock/conntrackd.lock

 UNIX {
  Path /var/run/conntrackd.sock
  Backlog 20
 }

 SocketBufferSize 262142
 SocketBufferSizeMaxGrown 655355

 # default debian service unit file is of Type=notify
 Systemd on
}

Stats {
 LogFile on
}

Helper {
 Type rpc inet udp {
                QueueNum 1
  QueueLen 10240
                Policy rpc {
                        ExpectMax 1
                        ExpectTimeout 300
                }
        }
        Type rpc inet tcp {
                QueueNum 2
  QueueLen 10240
                Policy rpc {
                        ExpectMax 1
                        ExpectTimeout 300
                }
        }
}

nfct list helper
{
 .name = rpc,
 .queuenum = 2,
 .l3protonum = 2,
 .l4protonum = 6,
 .priv_data_len = 0,
 .status = enabled,
};
{
 .name = rpc,
 .queuenum = 1,
 .l3protonum = 2,
 .l4protonum = 17,
 .priv_data_len = 0,
 .status = enabled,
};

iptables rule:
-A OUTPUT -d 10.0.0.0/24 -p udp -m udp --dport 111 -m comment --comment "Load RPC user space helper for outgoing calls to RPC on other local machines (See /etc/conntrackd/conntrackd.conf)" -j CT --helper rpc
-A OUTPUT -d 10.0.0.0/24 -p tcp -m tcp --dport 111 -m comment --comment "Load RPC user space helper for outgoing calls to RPC on other local machines (See /etc/conntrackd/conntrackd.conf)" -j CT --helper rpc

syslog:

Nov 16 15:06:54 mx systemd[1]: Started Conntrack Daemon.
Nov 16 15:06:54 mx conntrack-tools[17623]: netlink event socket buffer size has been set to 262142 bytes
Nov 16 15:06:54 mx conntrack-tools[17623]: configuring helper `rpc' with queuenum=2 and queuelen=10240
Nov 16 15:06:54 mx conntrack-tools[17623]: policy name=rpc expect_timeout=300 expect_max=1
Nov 16 15:06:54 mx conntrack-tools[17623]: helper `rpc' configured successfully
Nov 16 15:06:54 mx conntrack-tools[17623]: configuring helper `rpc' with queuenum=1 and queuelen=10240
Nov 16 15:06:54 mx conntrack-tools[17623]: policy name=rpc expect_timeout=300 expect_max=1
Nov 16 15:06:54 mx conntrack-tools[17623]: helper `rpc' configured successfully
Nov 16 15:06:54 mx conntrack-tools[17623]: initialization completed
Nov 16 15:06:54 mx conntrack-tools[17623]: -- starting in console mode --
Nov 16 15:07:12 mx kernel: [73016.216826] conntrackd[17623]: segfault at 4 ip 00007f7a25091eab sp 00007ffee3341cb0 error 6 in ct_helper_rpc.so[7f7a25091000+2000]