Have you tried deleting the config stored in the Karaf - via the OpenHab console? This worked for me.
See this post - item 8 -
Try to check with the Karaf Console (ssh openhab@localhost -p 8101 with password: habopen) what has been already stored in the OH2 “internal database” by using:
config:edit org.openhab.mqtt
config:property-list
Also, you can use: config:list to show you all bindings configs stored.
You can start clean by configuring your mqtt.cfg and mqtt-eventbus.cfg and clearing out whatever is stored already by:
config:delete org.openhab.mqtt and then restarting OH2 to reload the .cfg file