If there is parallel concurrent processing enabled then there might be the case that once we stop down the concurrent managers it will not come up when trying to start .
We may find the below error in the manager log which will state that manager is already running.
Routine &ROUTINE has attempted to start the internal concurrent manager.  The ICM is already running.  Contact you system administrator for further assistance.afpdlrq received an unsuccessful result from PL/SQL procedure or function FND_DCP.Request_Session_Lock.
Routine FND_DCP.REQUEST_SESSION_LOCK received a result code of 1 from the call to DBMS_LOCK.Request.
Possible DBMS_LOCK.Request resultCall to establish_icm failed
The Internal Concurrent Manager has encountered an error.
This is occoured due to locks in the Database.
1.Please use the below query to find the culprit SID .
select * from gv$session where program like '%ICM%'
2. Kill the SID and restart the Concurrent managers.
Oracle Note Id for more reference:Concurrent Processing – The Concurrent Manager Fails to Start on GSM Enabled Due to DBMS_LOCK.Request ResultCall Failed to Establish ICM [ID 245563.1]