To your knowledge credential-less discovery was never configured on your instance.
When running discovery or service mapping, credential-less discovery is still triggered.
Kingston or later
There is a property that controls credential-less discovery it is probably set to 'true'.
- Go to system properties (sys_properties)
- Search for name = mid.discovery.credentialless.enable
- If it has value 'true' change it to 'false' and save the record