The reason is likely that the application is mixing up its CDB and/or MAAPI sockets - e.g. two threads trying to use the same socket at the same time.
What it means is that a CDB or MAAPI API function makes a request to ConfD, and gets a response back from ConfD that doesn’t match the request.
The examples.confd/intro/9-c_threads/ example shows how one should handle these sockets when using multiple threads.