@Pashazadeh  Apache NiFI 2.0.x was a technical milestone/preview releases that underwent many changes before the first GA release with NiFi 2.1.x.  I would not expect a change in behavior going forward, unless some bug is introduced or the community agrees on a change in functionality/behavior.   While I don't have a specific answer to what bug resulted in the difference in behavior you encountered, here are some changes that affected the JsonRecordSetWriter. NIFI-14331 NIFI-13963 / NIFI-13843 NIFI-12670 If you still have your NiFi 2.0.0 running, you could run your flow using a convertRecord with same record readers and writers and then compare the output content with what you see with 2.7.1 output.  Maybe that can help figure out what is happening and if either of those bugs affecting earlier NiFi 2.x versions is related. Thanks, Matt ... View more