DB upgrade from 12.2.0.1 to 19.12 failed with possible reason not using CONNECT / AS SYSDBA

Hello,

My upgrade of 12.2.0.1 db to 19.12 failed due to possibly not connected as /as sysdba.  But I could not able to connect using /as sysdba from 19.12 ORACLE_HOME, I received the following error:

$ ./$ORACLE_HOME/bin/sqlplus /as sysdba

Enter user-name: /as sysdba

ERROR:

ORA-01017: invalid username/password; logon denied

DB host is Solaris 11.4 on SPARC 64bit with ODM setup using Veritas InfoScale 7.4.1.  

My question is why I could not connect /as sysdba from new 19.12 ORACLE_HOME to do the db upgrade?

Any hints or knowledge or experience share would appreciated. 

Larry