If there are problems in communication between NiFi Registry and Ranger, review the xa_secure.log and nifi-registry-app.log to determine the source of the issue. This might be due to certificates not being imported into the truststore of Ranger. Also, if Kerberos is not enabled, the commonNameForCertificate property value might be inaccurate.
The problem could also be due to certificates not being imported into NiFi Registry or the Ranger certificate not appropriately being identified. In addition to the previously mentioned logs, review the nifi-registry-user.log.