Performing SIGNAL_EVENT with invalid correlationKey under persistence=true for example. At first attempt, KnowledgeSession is created via KnowledgeSessionFactory.getPersistentSession(), and then the HandlerException is thrown since processInstanceId==null. This is expected behavior, however, BPMExchangeHandler.getBPMSession() throws SessionNotFoundException on redelivery. It even throws NPE after a few redeliveries. Apparently the KnowledgeSession may need to be cleaned up at first failure.