The 02-vyos-stopdhclient hook to find out all the running DHCP clients for a current interface uses the regex "/sbin/dhclient $ipversion_arg .*$interface$", but when dhclient is started by ifup (for example in images with Cloud-init), it generating the command:

/sbin/dhclient -4 -v -i -pf /run/dhclient.eth0.pid -lf /var/lib/dhcp/dhclient.eth0.leases -I -df /var/lib/dhcp/dhclient6.eth0.leases eth0 -e IF_METRIC=100

So it cannot be detected by the regex.

The regex should be modified to make it correct for this case too.