The file /etc/kafka/conf/server.properties that gets created after running the script upgradeHelper.py has the following property:
The value for this property is exactly the same in all the hosts running the kafka-broker, which causes the following exception in var/log/kafka/server.log
java.lang.IllegalArgumentException: requirement failed: Each listener must have a different port
The correct value for the listeners property should be HOST_NAME:PORT where HOST_NAME is the host name of the node corresponding to that kafka broker, and PORT is the kafka broker port
Please see attached screenshots for details.