An unexpected error has occurred while listing controller services on UI

[#1]

We have a NIFI cluster which have 3 nodes. All the nodes were working fine earlier. But now if all 3 nodes are connected to cluster and we right click on NIFI UI canvas and select "Configure" then we are getting error - "An unexpected error has occurred. Please check the logs for additional details." 

Below are more details fetched from network tabs on inspection on chrome. The same error can be found if we access NIFI UI using any node's hostname - 

1. Request URL:
   https://<node1>:<port>/nifi-api/flow/process-groups/{process_group_id}/controller-services
2. Request Method:
   GET
3. Status Code:
   500 Internal Server Error

If we disconnect node 3 from cluster then we are able to click on "Configure" and list all controller services on NIFI UI. Issue seems to be with node 3. We have synced flow.xml.gz file from node2 to other node ie.node1, node3 and also restarted the NIFI. But still the issue is there.
We have got this error in nifi-user.log -
"o.a.nifi.web.api.config.ThrowableMapper An unexpected error has occurred: java.lang.NullPointerException. Returning Internal Server Error response."
Our authorizers.xml and users.xml files are having same content across all 3 nodes. There was no issue of CPU, heap or memory also. Everything seems idle on all the nodes.
Please help us to resolve this issue.

[#2 · Accepted solution]

@sam_s0ni 

Verify that all 3 NiFi nodes are:

1. Running the exact same version of NiFI.
2. Running the exact same version of Java 8 or 11 (only supported by newest releases)
3. Contents of the NiFi lib directory, extensions directory, and any custom lib directories contain exact same content.

Try removing the NiFi work directory from all three nodes.  On restart NiFi will rebuild the contents of the work directory from above lib and extensions folders.

If you found this response assisted with your query, please take a moment to login and click on "Accept as Solution" below this post.

Thank you,

Matt