Github user mcgilman commented on the issue:
https://github.com/apache/nifi/pull/1582
I left this guidance on the JIRA for anyone testing/reviewing...
> Feel free to apply the server side changes first. This should prevent
NiFi from getting into this state. You should see an error indicating that you
cannot move a Process Group into itself. Then applying the UI changes, it
should make this sort of request impossible from the UI.
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