Why does a domain work for some people after a DNS change but not for others?

Different internet providers and devices can use different DNS resolvers, each with its own cached answer. After a record or nameserver change, one resolver may have the new destination while another still holds the previous value. This temporary inconsistency is common when the old record had a long time to live.

Local caches add another layer. The operating system, browser, router, VPN, or corporate network may remember an earlier response. Testing with a public resolver or another network can show whether the difference is local. Restarting every device is unnecessary if the upstream resolver still has a valid cached record.

The problem can also come from incomplete configuration. IPv4 and IPv6 records may point to different servers, or only one of the www and root names may have been updated. Split DNS on a company network, regional CDN behavior, or a missing domain binding on one server can produce a similar symptom.

Ask an affected user for the exact hostname, network, time, and resolved address. Compare that result with the authoritative records and the addresses of both old and new servers. Keep both environments working during the transition, and correct inconsistent A, AAAA, CNAME, or server-domain settings instead of repeatedly changing unrelated records.