Query DNS records directly instead of trusting the resolver cache.
dig
Ask a specific resolver
dig @1.1.1.1 example.com ABypass every cache on the path
dig +trace example.comShort answer with the useful bits
dig +short example.com A
dig +short MX example.comCompare answers across resolvers
for r in 1.1.1.1 8.8.8.8; do dig +short @$r example.com; doneIf the answer differs between resolvers, the host is not on a stable record. That is a DNS problem, not a server problem.