ORA-16706: Data Guard broker worker process not available
Thanks for comments for my doubts.

As now I have found a root cause and fix. 
Please find a fix: 

The Broker is killing the RSM0 process and restarting it because of an internal timeout that is too low. This can happen even in network choke condition also. 
Please provide what the OperationTimeout is set to.
DGMGRL> connect sys/
DGMGRL> show configuration OperationTimeout;

SOLUTION
Increase the OperationTimeout or apply the patch.
If this shows low 30-120, then set it higher, up to 600 (10 mins) :

DGMGRL> EDIT CONFIGURATION SET PROPERTY OperationTimeout=600;

Configuration - Dataguard_ABC

Protection Mode: MaxPerformance
  Databases:
  ABC_P - Primary database
    ABC_F - Physical standby database 
    ABC_D - Physical standby database 

Then works fine.