When JPAKnowledgeService.loadStatefulKnowledgeSession is called, it immediately starts processing any pending nodes. For instance, if any timers are due. But the problem comes, because it doesn't even give time to register any work item handlers. Usually sequence is:

• call loadStatefulKnowledgeSession
• register workitemhandlers
  But as soon you call loadStatefulKnowledgeSession, jbpm engine starts running and throws error because of missing workItemHandlers.

So jBPM should not start work flow processing on loadStatefulKnowledgeSession but some kind of resume method should be provided on StatefulKnowledgeSession class.