org.drools.RuntimeDroolsException during startup of BRMS 5.3.1

Issue

During the startup of our BRMS 5.3.1 servers we are sometimes facing the following exception:

org.drools.RuntimeDroolsException: Unexpected exception executing action org.jbpm.process.instance.event.DefaultSignalManager$SignalProcessInstanceAction@61492336
    at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:972)
    at org.drools.impl.StatefulKnowledgeSessionImpl.executeQueuedActions(StatefulKnowledgeSessionImpl.java:877)
    at org.jbpm.process.instance.event.DefaultSignalManager.signalEvent(DefaultSignalManager.java:90)
    at org.jbpm.process.instance.timer.TimerManager$ProcessJob.execute(TimerManager.java:318)
    at org.drools.time.SelfRemovalJob.execute(SelfRemovalJob.java:15)
    at org.drools.time.impl.DefaultTimerJobInstance.call(DefaultTimerJobInstance.java:47)
    at org.drools.persistence.jpa.JpaTimerJobInstance.internalCall(JpaTimerJobInstance.java:43)
    at org.drools.persistence.jpa.JDKCallableJobCommand.execute(JDKCallableJobCommand.java:20)
    at org.drools.persistence.jpa.JDKCallableJobCommand.execute(JDKCallableJobCommand.java:6)
    at org.drools.command.impl.DefaultCommandService.execute(DefaultCommandService.java:36)
    at org.drools.persistence.SingleSessionCommandService.execute(SingleSessionCommandService.java:360)
    at org.drools.persistence.jpa.JpaTimerJobInstance.call(JpaTimerJobInstance.java:34)
    at org.drools.persistence.jpa.JpaTimerJobInstance.call(JpaTimerJobInstance.java:14)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:98)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:206)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException
    at org.jbpm.process.audit.JPAWorkingMemoryDbLogger.getEntityManager(JPAWorkingMemoryDbLogger.java:172)
    at org.jbpm.process.audit.JPAWorkingMemoryDbLogger.persist(JPAWorkingMemoryDbLogger.java:191)
    at org.jbpm.process.audit.JPAWorkingMemoryDbLogger.addNodeExitLog(JPAWorkingMemoryDbLogger.java:156)
    at org.jbpm.process.audit.JPAWorkingMemoryDbLogger.logEventCreated(JPAWorkingMemoryDbLogger.java:97)
    at org.drools.audit.WorkingMemoryLogger.filterLogEvent(WorkingMemoryLogger.java:196)
    at org.drools.audit.WorkingMemoryLogger.beforeNodeLeft(WorkingMemoryLogger.java:506)
    at org.drools.event.ProcessEventSupport.fireBeforeNodeLeft(ProcessEventSupport.java:112)
    at org.jbpm.workflow.instance.impl.NodeInstanceImpl.triggerNodeInstance(NodeInstanceImpl.java:206)
    at org.jbpm.workflow.instance.impl.NodeInstanceImpl.triggerCompleted(NodeInstanceImpl.java:169)
    at org.jbpm.workflow.instance.impl.ExtendedNodeInstanceImpl.triggerCompleted(ExtendedNodeInstanceImpl.java:47)
    at org.jbpm.workflow.instance.node.StateBasedNodeInstance.triggerCompleted(StateBasedNodeInstance.java:162)
    at org.jbpm.workflow.instance.node.TimerNodeInstance.triggerCompleted(TimerNodeInstance.java:134)
    at org.jbpm.workflow.instance.node.TimerNodeInstance.signalEvent(TimerNodeInstance.java:124)
    at org.jbpm.workflow.instance.impl.WorkflowProcessInstanceImpl.signalEvent(WorkflowProcessInstanceImpl.java:338)
    at org.jbpm.process.instance.event.DefaultSignalManager$SignalProcessInstanceAction.execute(DefaultSignalManager.java:118)
    at org.drools.common.AbstractWorkingMemory.executeQueuedActions(AbstractWorkingMemory.java:970)
    ... 19 more

After this error no new tasks are getting created.