After adding and removing load-balancing configuration there's a PID that exists after the config removing.
This pid used in dhcp-exit-hook

So if we don't have load-balancing in the configuration it tries to send the user signal to not exist process kill -s SIGUSR2 xxx

To reproduce:

set load-balancing wan interface-health eth1 nexthop dhcp
commit
delete load-balancing
commit
run renew dhcp interface ethX

File exists after removing load-balancing

vyos@vyos2# file /var/run/vyatta/wlb.pid
/var/run/vyatta/wlb.pid: ASCII text

Log:

May 04 12:55:14 vyos2 root[8725]: /etc/dhcp/dhclient-exit-hooks.d/04-dhcp-wanlb returned non-zero exit status 1

Propose to use OR in the hook or remove the PID properly

kill -s SIGUSR2 $( cat $pid ) 2>/dev/null => kill -s SIGUSR2 $( cat $pid ) 2>/dev/null || true