Did this get resolved for the OP? I just setup a new ER-X-SFP on 1.9.0 using the GUI/wizard and everything was working fine when it came to IPv6. However, after enabling hwnat offload, IPv6 isn't working for me either. My config:
firewall { all-ping enable broadcast-ping disable ipv6-name WANv6_IN { default-action drop description "WAN inbound traffic forwarded to LAN" enable-default-log rule 10 { action accept description "Allow established/related sessions" state { established enable related enable } } rule 20 { action drop description "Drop invalid state" state { invalid enable } } } ipv6-name WANv6_LOCAL { default-action drop description "WAN inbound traffic to the router" enable-default-log rule 10 { action accept description "Allow established/related sessions" state { established enable related enable } } rule 20 { action drop description "Drop invalid state" state { invalid enable } } rule 30 { action accept description "Allow IPv6 icmp" protocol ipv6-icmp } rule 40 { action accept description "allow dhcpv6" destination { port 546 } protocol udp source { port 547 } } } ipv6-receive-redirects disable ipv6-src-route disable ip-src-route disable log-martians enable name WAN_IN { default-action drop description "WAN to internal" rule 10 { action accept description "Allow established/related" state { established enable related enable } } rule 20 { action drop description "Drop invalid state" state { invalid enable } } } name WAN_LOCAL { default-action drop description "WAN to router" rule 10 { action accept description "Allow established/related" state { established enable related enable } } rule 20 { action drop description "Drop invalid state" state { invalid enable } } } receive-redirects disable send-redirects enable source-validation disable syn-cookies enable } interfaces { ethernet eth0 { address dhcp description Internet dhcpv6-pd { pd 0 { interface switch0 { host-address ::1 prefix-id :1 service slaac } prefix-length /60 } rapid-commit enable } duplex auto firewall { in { ipv6-name WANv6_IN name WAN_IN } local { ipv6-name WANv6_LOCAL name WAN_LOCAL } } speed auto } ethernet eth1 { description Local duplex auto poe { output 24v } speed auto } ethernet eth2 { description Local duplex auto speed auto } ethernet eth3 { description Local duplex auto speed auto } ethernet eth4 { description Local duplex auto speed auto } ethernet eth5 { duplex auto speed auto } loopback lo { } switch switch0 { address 192.168.1.1/24 description Local mtu 1500 switch-port { interface eth1 { } interface eth2 { } interface eth3 { } interface eth4 { } vlan-aware disable } } } service { dhcp-server { disabled false hostfile-update disable shared-network-name LAN { authoritative enable subnet 192.168.1.0/24 { default-router 192.168.1.1 dns-server 192.168.1.1 lease 86400 start 192.168.1.38 { stop 192.168.1.243 } } } use-dnsmasq disable } dns { forwarding { cache-size 150 listen-on switch0 } } gui { http-port 80 https-port 443 older-ciphers enable } nat { rule 5010 { description "masquerade for WAN" outbound-interface eth0 type masquerade } } ssh { port 22 protocol-version v2 } } system { host-name ubnt login { user admin { authentication { encrypted-password } level admin } } ntp { server 0.ubnt.pool.ntp.org { } server 1.ubnt.pool.ntp.org { } server 2.ubnt.pool.ntp.org { } server 3.ubnt.pool.ntp.org { } } offload { hwnat enable } syslog { global { facility all { level notice } facility protocols { level debug } } } time-zone America/Los_Angeles traffic-analysis { dpi enable export enable } }