Github user mattyb149 commented on the issue:
https://github.com/apache/nifi/pull/2175
Failure in the case of not-found-while-deleting is subjective IMO. You can
look at it as "the processor did not perform the task I issued", or "the
processor accomplished the end goal of the task (i.e. the document is not there
after the delete)". It seems ES is choosing the latter, but if a general user
would expect a "failed delete" along the failure relationship, we can treat
them as such.---
