Multiple Instance: How to obtain LoopCounter in External tasks?

I have started 5 external tasks in Multiple Instance mode (parallel).
How can I get the loopCounter variable for this external-task? I try to get variable by ExternalTask.ExecutionId but there is no data.

I see loopCounter variable that linked to the parent execution of ExternalTask.ExecutionId. But I can’t to get the parentExecutionId via code…

What’s wrong?