Although 2 nodes showing connected , we should also see the time stamps under column started At and LastHearbeat . also I am expecting to see coordinator and primary under status column.
it is not clear from attached snap, as in from which node you are trying to access the UI ? if you open UI from each node 1,2, and 3 what you see? Is 3rd is showing as disconnected ?
have you checked the process id's of nifi on 3rd node?
How zookeeper is used ? External user or embedded zookeeper ?