Some domain names with ultralow servers (with IPv6) are not being resolved

Hi,

Recently, I noticed that ultralow servers with IPv6 (specifically greencloud-sgn) are not resolving some domain names (e.g., grc.com, dnsleaktest.com, etc.). Many people in Vietnam have also complained about this issue. Here are the details:

* Greencloud-sgn (with IPv6):

Output https://dns.nextdns.io/info

{"locationName": "🇻🇳 Ho Chi Minh, Viet Nam", "pop": "greencloud-sgn", "rtt": 7996}

When accessing the domains grc.com and dnsleaktest.com, both result in an ERR_NAME_NOT_RESOLVED error (when using the Edge browser). Other browsers such as Chrome/Firefox also show an error indicating the page cannot be found.

* Lightnode-sgn (IPv4 only):

Output https://dns.nextdns.io/info

{"locationName": "🇻🇳 Ho Chi Minh, Viet Nam", "pop": "lightnode-sgn", "rtt": 95827}

If my browser switches to a different server (without IPv6), both websites are accessible normally.

* Additional information

- I used the DNSSEC checker tool to check the domain name, and the results showed that all authoritative DNS servers responded normally. Therefore, I ruled out the possibility that the authoritative DNS servers were experiencing problems.

• grc.com: https://dnssec-analyzer.verisignlabs.com/grc.com & https://dnsviz.net/d/grc.com/dnssec/
• dnsleaktest.com: https://dnssec-analyzer.verisignlabs.com/dnsleaktest.com & https://dnssec-analyzer.verisignlabs.com/dnsleaktest.com

- If I check the DNS server from https://browserleaks.com/dns, it only recognizes the IPv6 address of the greencloud-sgn server.

I suspect that the ultralow server is only resolving DNS on IPv6, which is causing this error.

Hopefully NextDNS will check and fix it! Thanks!