About the DNS Propagation Checker
The DNS Propagation Checker queries the same record through three independent resolvers — Google 8.8.8.8, Cloudflare 1.1.1.1 (both via DNS-over-HTTPS) and this server's local resolver — and tells you whether the answers already match. The fastest way to see if a DNS change has gone live everywhere or is still stuck in caches. For the full record set of one resolver, use the DNS Lookup.
Until every cache worldwide has expired the old TTL — typically minutes to a few hours with low TTLs, up to 48h worst case. New lookups get the fresh value immediately; caches keep the old one until their TTL runs out.
During a change: normal, that IS propagation. Permanently different answers usually mean GeoDNS/CDN (intentional) or a forgotten secondary name server (a problem).
Google Public DNS (8.8.8.8) and Cloudflare (1.1.1.1) via their DNS-over-HTTPS JSON APIs, plus this server's own resolver — three independent views on your record.