The dhcpv6 client can be running to manage the interface address, but it can also be running to manage "parameters-only" and/or prefix-delegations. It can be useful to restart the client even if it's not managing the interface address, but the current code gates on the presence of address dhcpv6 in the config:
set interfaces ethernet eth0 address 'dhcp' set interfaces ethernet eth0 dhcpv6-options parameters-only set interfaces ethernet eth0 dhcpv6-options pd 0 interface dum4 address '1' set interfaces ethernet eth0 dhcpv6-options pd 0 interface dum4 sla-id '5' set interfaces ethernet eth0 dhcpv6-options pd 0 length '56' set interfaces ethernet eth0 dhcpv6-options rapid-commit set interfaces ethernet eth0 ipv6 address autoconf $ renew dhcpv6 interface eth0 DHCPv6 client not configured on interface eth0!