@Rob_Pope I had a similar problem in the past… It was due to OpenHab 2 loading up the default mqtt.cfg config file (with the sample <broker> name)… it was my mistake since I removed the comments from the lines without adjusting the broker name… After I fixed the mistake, the <broker> info still remained (as a second broker) in OH2 “internal database” (I don’t know how to call it :)) and was causing errors because all other parameters for <broker> were null.
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 files
BR,
Dim