ERROR_READ_MSG_TIMEOUT(-12099) This explains the causes and corrective actions for the error.

--sys.log contents
[11-19T10:19:57.412159] [FRM-233] [I] ERROR_READ_MSG_TIMEOUT(-12099) during a user authentication process. client ip:***.***.***.77, port:59753, prog_name:, user_name:, osuser_name:, terminal:
[11-19T10:19:57.414319] [FRM-234] [I] ERROR_READ_MSG_TIMEOUT(-12099) during a user authentication process. client ip:***.***.***.77, port:59754, prog_name:, user_name:, osuser_name:, terminal:
[11-19T10:19:57.414610] [CSC-238] [W] timeout from client ***.***.***.77:59758
[11-19T10:19:57.414704] [FRM-238] [I] ERROR_READ_MSG_TIMEOUT(-12099) during a user authentication process. client ip:***.***.***.77, port:59758, prog_name:, user_name:, osuser_name:, terminal:

Cause

ERROR_READ_MSG_TIMEOUT(-12099) Error Explanation

 When a client requests a connection to the server, a WTHR (Working Thread) is assigned and before the session opens, the authentication process is as follows.

   1) The WTHR sends a Greeting Message to the client.  
       The Greeting Message contains information such as DB Version and DB Character Set.  

   2) The WTHR waits to receive the Authentication Message from the client.

   3) The client receives the Greeting Message and sends the agreed Authentication Message.
       The Authentication Message contains information such as Username and Password.

      3-1) When the WTHR receives the Authentication Message from the client, it goes through procedures such as message protocol validation and username/password verification, then the session opens.

      3-2) If the client does not send the Authentication Message, after waiting a certain period, a timeout occurs and
            ERROR_READ_MSG_TIMEOUT(-12099) error occurs, and the connection between the WTHR and client is terminated.

      3-3) If the client does not send the Authentication Message and disconnects, an ERROR_IO(-18017) error occurs 
             and the connection between the WTHR and client is terminated.

Solutions

ERROR_READ_MSG_TIMEOUT(-12099) Error Handling

 AUTHENTICATION_TIMEOUT parameter setting can extend the server’s waiting time to receive the Authentication Message from the client to mitigate this error. However, if there is a fundamental cause, the error will recur, so it is necessary to check for IP duplication on the network or inspect firewalls and security solutions.

--Parameter setting method (can be changed dynamically)  
1. Connect to tbsql as SYS
   SQL> ALTER SYSTEM SET AUTHENTICATION_TIMEOUT=100;
        System altered.

2. To apply on reboot, add to the initialization parameter file
   $ vi $TB_HOME/config/$TB_SID.tip 
     AUTHENTICATION_TIMEOUT=100