The following exception was seen when an OAM Stop was sent while OAM Start was being processed.

2017-10-04T01:33:27.030Z|R3798stop-Step12|qtp1232998187-116 - /restconf/operations/appc-oam:stop|stop|ECOMP-Controller|APPC|APPC OAM Provider|ERROR|200|UNEXPECTED ERROR - java.util.ConcurrentModificationException|APPC0153E Application APPC received exception ConcurrentModificationException while attempting to execute oam operation stop, exception message = java.util.ConcurrentModificationException
Exception ConcurrentModificationException: null
    at java.util.HashMap$KeySpliterator.forEachRemaining(HashMap.java:1553)
    at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
    at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
    at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
    at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
    at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    ... 74 more frames

The OAM Start was Aborted but OAM Stop did not start and the APPC is in state "stopping"