What could cause mysql-router to not open/listen to port 6446 when running as a daemon?

Question

I have a 3 primary node innodb cluster setup which is running as expected. To connect to these I have mysql-router setup, however, when running mysql-router as a daemon service mysql-router start it does not open/listen to port 6446, 6447 or 6448. I can only get mysql-router running when running as a command line mysqlrouter -c /etc/mysqlrouter/mysqlrouter.conf

Here is a dump of mysqlrouter daemon script

. /lib/lsb/init-functions

DESC="Start / Stop MySQL Router"
DAEMON=/usr/bin/mysqlrouter
DAEMON_OPTIONS="-c /etc/mysqlrouter/mysqlrouter.conf"
NAME="MySQL Router"
RUNTIMEDIR=/var/run/mysqlrouter/
PID=${RUNTIMEDIR}/mysqlrouter.pid
STOP_RETRY=3
LOGDIR=/var/log/mysqlrouter
LOGFILE=${LOGDIR}/mysqlrouter.log
DATADIR=/var/lib/mysqlrouter

do_start() {

  local retval=0
  log_daemon_msg "Starting MySQL Router"

  if [ ! -x $DAEMON ]; then
    log_end_msg 1
    return 0
  fi

  if [ ! -d ${RUNTIMEDIR} -a ! -L ${RUNTIMEDIR} ];
  then
    install -d -m 0750 -o mysqlrouter -g adm ${RUNTIMEDIR}
  fi

  if [ ! -d ${DATADIR} -a ! -L ${DATADIR} ];
  then
    install -d -m 0750 -o mysqlrouter -g adm ${DATADIR}
  fi

  if [ ! -d ${LOGDIR} -a ! -L ${LOGDIR} ];
  then
    install -d -m 0750 -o mysqlrouter -g adm ${LOGDIR}
    install /dev/null -m 0640 -o mysqlrouter -g adm ${LOGFILE}
  fi

  [ -x /lib/init/apparmor-profile-load ] && /lib/init/apparmor-profile-load usr.bin.mysqlrouter

  start-stop-daemon --start \
    --pidfile $PID \
    --startas $DAEMON \
    --oknodo \
    --make-pidfile \
    --background \
    --chuid mysqlrouter \
    -- $DAEMON_OPTIONS 2>/dev/null
  retval=$?

  case $retval in
    0) log_end_msg 0 ;;
    1)
      log_warning_msg "already running"
      log_end_msg 0
      ;;
    2) log_end_msg 1 ;;  # failure
  esac

  return $retval
}

do_stop() {
  local retval

  log_daemon_msg "Stopping $NAME"

  if [ ! -x $DAEMON ]; then
    log_end_msg 1
    return 0
  fi

  start-stop-daemon --stop \
    --pidfile $PID \
    --startas $DAEMON \
    --quiet \
    --retry=$STOP_RETRY
  retval=$?

  case $retval in
    0)
      log_end_msg 0
      ;;
    1)
      log_warning_msg "not running"
      log_end_msg 255
      ;;
    *) log_end_msg 1 ;;
  esac

  return $retval
}

do_status() {
  status_of_proc -p $PID $DAEMON "$NAME"
}

case "$1" in
  start)
    do_start
    ;;
  status)
    do_status
    ;;
  restart|force-reload)
    do_stop
    sleep 1
    do_start
    ;;
  stop)
    do_stop
    sleep 1
    ;;
  *)
    >2& echo "Usage: /etc/init.d/mysqlrouter {start|stop|status|restart|force-reload}"
    exit 3
esac