AutoUpgrade fails in POSTFIXUP phase of RAC DB Upgrade (Doc ID 2575477.1)

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ORA-00603: ORACLE server session terminated by fatal error
ORA-01092: ORACLE instance terminated. Disconnection forced
ORA-39701: database must be mounted EXCLUSIVE for UPGRADE or DOWNGRADE
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upg> status
---------------- Config -------------------
User configuration file [/xxx/xxxxxx/xxx/xxx/xxxxx/xxxx/new.cfg]
General logs location [/xxx/xxxxxx/xxx/xxx/xxxxx/xxxx]
Mode [DEPLOY]
DB upg fatal errors ORA-00600,ORA-07445
DB Post upgrade abort time [60] minutes
DB upg abort time [1440] minutes
DB restore abort time [120] minutes
DB drop GRP abort time [3] minutes
------------------------ Jobs ------------------------
Total databases in configuration file [1]
Total Non-CDB being processed [1]
Total CDB being processed [0]
Jobs finished successfully [0]
Jobs finished/aborted [0]
Jobs in progress [1]
Jobs stage summary
Job ID: 100
DB name: xxxx_xxxxxxx
SETUP <1 min
PREUPGRADE <1 min
PRECHECKS <1 min
PREFIXUPS <1 min
DRAIN <1 min
DBUPGRADE 33 min
POSTCHECKS 1 min
POSTFIXUPS 69 min (IN PROGRESS)             <<<====
---------------

2019-07-08 11:33:46.947 INFO SUCCESSFULLY UPGRADED [xxx_xxxxxx] 
2019-07-08 11:33:46.947 INFO End Upgrade on Database [xxxx_xxxxxx] 
2019-07-08 11:34:14.417 INFO Begin Compiling Invalid Objects on Database [xxxx_xxxxxxx] 
2019-07-08 11:35:57.491 INFO [Compiling] is [0%] completed for [xxxx_xxxxxxxxx] objects remaining is [44]
+-----------------+------------+
|        CONTAINER|  PERCENTAGE|
+-----------------+------------+
|MIGDB_RB0TSTRAC01|COMPILE [0%]|
+-----------------+------------+ 
2019-07-08 11:36:34.428 INFO End Compiling Invalid Objects on Database [xxxx_xxxxxxxxx] 
2019-07-08 11:36:34.429 INFO SUCCESSFULLY COMPILED [xxxx_xxxxxxxxx] 
2019-07-08 11:36:37.493 INFO [Upgrading] is [100%] completed for [xxxx_xxxxxxxxx] 
+-----------------+-----------------------------------------+
|        CONTAINER|                               PERCENTAGE|
+-----------------+-----------------------------------------+
|MIGDB_RB0TSTRAC01|SUCCESSFULLY UPGRADED [xxxx_xxxxxxxxx]|
+-----------------+-----------------------------------------+ 
2019-07-08 11:36:37.516 INFO Error opening file [/xxx/xxxxxx/xxx/xxx/xxxxx/xxxx/dbs/inixxxxxx.ora] for reading. 
2019-07-08 11:36:38.542 INFO Creating spfile completed with success 
2019-07-08 11:36:38.543 INFO SUCCESSFULLY UPGRADED [xxx_xxxxx] 
2019-07-08 11:36:38.559 INFO xxxx_xxxxxxxxx Return status is SUCCESS 
2019-07-08 11:38:46.999 INFO Analyzing xxxx_xxxxxxxxx, 7 checks will run using 7 threads 
2019-07-08 11:38:52.988 INFO Using /xxx/xxxxxx/xxx/xxx/xxxxx/xxxx/logs/xxxxx/100/prechecks/xxxx_xxxxx_checklist.cfg as reference to determine the fixups which will be executed 
2019-07-08 11:41:15.101 INFO Executing [/xxx/xxxxxx/xxx/xxx/xxxxx/xxxx/logs/xxxx/xxxx/temp/sqlsessstart.sql][xxxx_xxxxxxxx] 
2019-07-08 11:41:15.101 INFO Complete [/xxx/xxxxxx/xxx/xxx/xxxxx/xxxx/logs/xxxx/xxxx/temp/sqlsessstart.sql][xxxx_xxxxxxxx] 
2019-07-08 11:41:15.602 INFO Executing [/xxx/xxxxxx/xxx/xxx/xxxxx/xxxx/logs/xxxx/xxxx/temp/xxx_xxxxxx_utltz_upg_check.sql][xxxx_xxxxxxxx] 
2019-07-08 11:41:15.602 INFO Complete [/xxx/xxxxxx/xxx/xxx/xxxxx/xxxx/logs/xxxx/xxxx/temp/xxx_xxxxxx_utltz_upg_check.sql][xxxx_xxxxxxxx] 
2019-07-08 11:41:17.603 INFO Executing /xxx/xxxxxx/xxx/xxx/xxxxx/xxxx/logs/xxxx/xxxx/temp/xxx_xxxxxx_utltz_upg_apply.sql][xxxx_xxxxxxxx] 
2019-07-08 11:41:17.603 INFO Complete [/xxx/xxxxxx/xxx/xxx/xxxxx/xxxx/logs/xxxx/xxxx/temp/xxx_xxxxxx_utltz_upg_apply.sql][xxxx_xxxxxxxx]