When you are able to resolve a domain in one region of the world, but not another, the problems are often due to connectivity issues.
https://zonalizer.makeinstall.se/?knvbBywLQdCflUWk3ONwAQ reports that all the name servers for vultr.com are in a single AS, and it is possible that Google's connectivity to that network was lost in parts of Asia.
You may want to consider adding secondary DNS service from other providers, e.g. https://www.keycdn.com/blog/best-free-dns-hosting-providers/
offers very good coverage, and is free: you would need to enter the he.net
nameserver IP (220.127.116.11) to the AXFR allowed whitelist of your primary nameserver, and then add the he.net
nameservers and/or replace some of the duplicate nameservers on your single subnet with he.net
nameservers in your domain registration.
That Zonalizer report also shows that the .COM TLD lists these name servers and IP addresses:
;; AUTHORITY SECTION:
vultr.com. 172800 IN NS ns1.vultr.com.
vultr.com. 172800 IN NS ns2.vultr.com.
;; ADDITIONAL SECTION:
ns1.vultr.com. 172800 IN A 18.104.22.168
ns1.vultr.com. 172800 IN AAAA 2001:19f0:ccd::1
ns2.vultr.com. 172800 IN A 22.214.171.124
ns2.vultr.com. 172800 IN AAAA 2001:19f0:ccd::2
while the NS records at the vultr.com name servers show a different set of name servers and IP addresses.
ns1.choopadns.com 17 A 126.96.36.199
ns1.choopadns.com 599 AAAA 2001:19f0:ccc::1
ns2.choopadns.com 44 A 188.8.131.52 [AS20473]
ns2.choopadns.com 599 AAAA 2001:19f0:ccc::2
Google Public DNS will only use the name server names listed in the .COM TLD registry, for best results generally, you should configure the delegation records in the TLD to match the names in the zone itself, making sure that all listed name servers are able to respond successfully to queries for the zone.