OEM Agent Throws Error “Internal error detected: oracle.sysman.gcagent.task.TaskZombieException:oracle.sysman.gcagent.task.TaskFutureImpl$WrappedTask:620”

In OEM 13c, a couple of OEM agents reported some internal errors  like :

Internal error detected: oracle.sysman.gcagent.task.TaskZombieException:oracle.sysman.gcagent.task.TaskFutureImpl$WrappedTask:620

Internal error detected: oracle.sysman.gcagent.task.TaskZombieException:oracle.sysman.gcagent.task.TaskFutureImpl$WrappedTask:621

From: oracle 
Sent: Monday, 13 February 2017 10:41 AM
To: 
Subject: EM Event: Critical:ractest:3872 - Internal error detected: oracle.sysman.gcagent.task.TaskZombieException:oracle.sysman.gcagent.task.TaskFutureImpl$WrappedTask:620.

Host=ractest
Target type=Agent 
Target name=ractest:3872 
Categories=Diagnostics 
Message=Internal error detected: oracle.sysman.gcagent.task.TaskZombieException:oracle.sysman.gcagent.task.TaskFutureImpl$WrappedTask:620. 
Severity=Critical 
...
..
.
Update Details:
Internal error detected: oracle.sysman.gcagent.task.TaskZombieException:oracle.sysman.gcagent.task.TaskFutureImpl$WrappedTask:620.

Extracted from gcagent.log :

2017-02-13 10:10:00,329 [256:7761FFD4] WARN - IntervalSchedule: Skip schedule [rac_database:RACTEST:observer_11g] - skipping due to execution time exceeding interval
2017-02-13 10:10:00,329 [257:B85D2018:GC.Executor.6 (oracle_database:RACTEST:Response)] WARN - IntervalSchedule: Skip schedule [oracle_database:RACTEST:Response] - skipping due to execution time exceeding interval
2017-02-13 10:10:00,329 [258:5A4306F7:GC.Executor.7 (rac_database:RACTEST:observer_11g)] WARN - Action result processing failure rac_database.RACTEST::observer_11g
java.lang.InterruptedException 
 at java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireSharedNanos(AbstractQueuedSynchronizer.java:1302)
...
..
.
oracle.sysman.gcagent.task.TaskZombieException: task declared as a zombie
 at oracle.sysman.gcagent.task.TaskFutureImpl$WrappedTask.accountedCall(TaskFutureImpl.java:620)
 at oracle.sysman.gcagent.task.TaskFutureImpl$WrappedTask.call(TaskFutureImpl.java:643)
 at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
 at java.util.concurrent.FutureTask.run(FutureTask.java:138)
 at oracle.sysman.gcagent.task.TaskFutureImpl.run1(TaskFutureImpl.java:380)
...
..
. 

 at java.lang.Thread.run(Thread.java:662)
2017-02-13 10:10:00,331 [257:GC.Executor.6] ERROR - Critical error:
oracle.sysman.gcagent.task.TaskZombieException: task declared as a zombie
 at oracle.sysman.gcagent.task.TaskFutureImpl$WrappedTask.accountedCall(TaskFutureImpl.java:620)
 at oracle.sysman.gcagent.task.TaskFutureImpl$WrappedTask.call(TaskFutureImpl.java:643)

WORKAROUND