@Benjamin HoppWhat reason if NiFi giving in the nifi-app.log for the node disconnections?
Rather then restarting the node that disconnects, did you try just clicking the reconnect icon in the cluster UI?

Verify that your nodes do not have trouble communicating with each other. Makes there are no firewalls between the nodes affecting communications to the HTTP/HTTPS ports:
nifi.web.http.host=nifi-ambari-08.openstacklocal
nifi.web.http.port=8090
nifi.web.https.host=nifi-ambari-08.openstacklocal
nifi.web.https.port=9091
or node communication port:
nifi.cluster.node.address=nifi-ambari-08.openstacklocal
nifi.cluster.node.protocol.port=9088
Make sure Both yo r nodes are properly configured to talk to ZK and neither has issues communicating with them:
nifi.zookeeper.connect.string=nifi-ambari-09.openstacklocal:2181,nifi-ambari-07.openstacklocal:2181,nifi-ambari-08.openstacklocal:2181
nifi.zookeeper.connect.timeout=3 secs
nifi.zookeeper.root.node=/nifi
nifi.zookeeper.session.timeout=3 sec
All of the above setting are in the nifi.properties file.
Thanks,
Matt