I found my problem. The previous code I uploaded was still using Mina Service. I did modification below so to use LocalTaskService. Now it is working, no need to Thread.sleep(1000) any more. :)
TaskService localTaskService = new LocalTaskService(taskSession);
SyncWSHumanTaskHandler syncWSHumanTaskHandler = new SyncWSHumanTaskHandler(localTaskService, ksession);
syncWSHumanTaskHandler.setLocal(true);
syncWSHumanTaskHandler.setClient(localTaskService);