@venkii 

What version of NiFi are you running?

There are a set of bugs identified here that are likely related to the issue you described:
https://issues.apache.org/jira/browse/NIFI-5948
https://issues.apache.org/jira/browse/NIFI-6020
https://issues.apache.org/jira/browse/NIFI-6027

The good news is that these have all since been resolved.  
I would recommend upgrading your NiFi to a version 1.10 or newer.
Or HDF 3.4.1.1 or newer
Or CFM 1.0.1 or newer

As a workaround, you could shutdown you NiFi and search the users.xml and authorizations.xml file for uuid "938eb61e-bbc4-383a-8475-aee80541b5a5" and remove all references to it.  You would then need to make the exact same changes to the users.xml and authorizations.xml file on every other node in your NiFi cluster or copy the corrected files from one node to the other nodes.

Hope this helps,

Matt