Does the router still have IPv6 connectivity to the WAN or is it just the clients that have lost connectivity?
I see on eth4 you have the Router Advertisement 'managed' flag set as true. Do you have an IPv6 DHCP server or are the clients using SLAAC for their IPv6 addresses? If you don't have an IPv6 DHCP server then try set interfaces ethernet eth4 ipv6 router-advert managed-flag false.
Regards