AAAA record

The record that holds an IPv6 address, what the A record is for IPv4. Publish one only if the server really answers on that address: a wrong AAAA is worse than no AAAA at all. IPv6 clients prefer it and try it ahead of the A. Those visitors fail while everyone else succeeds, which reads as an "intermittent" outage nobody can reproduce from an IPv4 machine, and gets blamed on the application. dig +short example.com AAAA shows what you published; curl -6 -I https://example.com proves the server answers there. If the machine has no IPv6, publishing no AAAA is the consistent choice and nothing breaks. The listen [::]:80 line in the server block is the other half: the record and the listening socket have to agree.