I had problems with native ipv6 and found a setting in TOOLS/WAN: Use local caching dns server system resolver. I changed that setting to yes and rebooted. Native IPV6 was then working.
You might see if that setting helps
I had problems getting native IPV6 to work. I wound up finding a setting in TOOLS/OTHER SETTINGS/ Wan: Use local caching DNS server as system resolver. I selected yes and rebooted. IPV6 then began working.
I had problems with ipv6 and found a setting that fixed it for me. Tools/other settings/under advanced tweaks and hacks-WAN:Use local caching DNS Server-change it from NO to YES.