When using many same rules with after, event expiration cycles itself.
Using 64 copies of this rule [1], code here [2] cycles itself. I think it is because when it searches through child and peer tuples, it can find already expired tuple and it tries to expire it again. So the problem is either there or in that there is some cycle in tuple chain.

The commit with code from [2] is part of 6.3.2.CR1 tag sync-6.4.x-2016.07.07.

Reproducer attached in PR in linked upstream issue.

[1]
import org.drools.testcoverage.common.model.EventA;
import org.drools.testcoverage.common.model.EventB;
declare org.drools.testcoverage.common.model.EventA @role( event ) @duration(duration) end declare org.drools.testcoverage.common.model.EventB @role( event ) @duration(duration) end rule R0 when
$event1: org.drools.testcoverage.common.model.EventA()
$event2: org.drools.testcoverage.common.model.EventB(this != $event1, this after [1,10] $event1)
then end
[2] https://github.com/droolsjbpm/drools/blob/6.4.x/drools-core/src/main/java/org/drools/core/impl/StatefulKnowledgeSessionImpl.java#L1820