I saw a couple of messages like this in an Oracle listener log recently:
TNS-01189: The listener could not authenticate the user
I knew that somebody in another country was carrying out internal security scans and suspected this may have been the reason. To confirm, I tried to check the status of the listener from another server and was able to reproduce the error as follows:
UNIX: lsnrctl status 10.80.1.150:1529
LSNRCTL for Solaris: Version 11.2.0.1.0 - Production on 05-SEP-2019 10:22:57
Copyright (c) 1991, 2009, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(CONNECT_DATA=(SERVICE_NAME=))(ADDRESS=(PROTOCOL=TCP)(HOST=10.80.1.150)(PORT=1529)))
TNS-01189: The listener could not authenticate the user
UNIX: