Again, you don't need to Inject the TaskService if you have the runtime manager. Also if you are using @PerProcessInstance you shouldn't call the variable singletonManager.
It seems that you are creating multiple times the JbpmService which causes to create multiple instances of the RuntimeManager, so you need to make sure that the JbpmService is not instantiated more than once.
The injected TaskService is old...
Now Im getting it from the RuntimeEngine
Thanks for the answer!