I'm having this issue to. When I check nextdns, cloudflare, google for ip6.[hash].myunraid.net I just "get couldn't find ip6.[hash].myunraid.net. Is there a problem with the DDNS service and AAAA records right now?
If I turn off ipv6 on my interface then reboot it defaults to X-X-X-X.[hash].myunraid.net and works fine with ipv4.