X_READINESS_CHECK_DUPLICATE
Means
a readiness check name is registered twice
Typical cause
two registerReadinessCheck('<name>', check) calls under one name. A silent replacement leaves the probe an operator believes is running unreachable, and /readyz green on the strength of the one that replaced it — the cause lists every name already registered
Fix
name the second check for what it actually probes, e.g. registerReadinessCheck('<name>-replica', check) — or hold the unregister the first registration returned and call it first