Here is the reply from the support team about this issue:
In a Self-signed SSL Certificate, the Common Name value used for the server and client certificates/keys must each differ from the Common Name value used for the CA certificate.
You get this error as the Common Name value for the server and client certificates/keys and the CA certificate are the same.
This was not enforced in the client library we used before 12.2.6. However if names don’t differ you wll be vulnerable to ‘man in the middle’ -attacks. So this won’t be reverted.