I have a fresh installation on RPI2. I added MQTT binding in paperUI. It did not work because I did not configure mqtt.cfg.
So I followed some instruction on how to fix that. I had double entries in Karaf console, so I deleted them. Restarted openhab, and now I have NO activity in openhab.log about mqtt:
Befora I had at least
2017-09-19 21:53:20.190 [INFO ] [t.mqtt.internal.MqttBrokerConnection] - Starting MQTT broker connection ‘mymqtt’
Now there is nothing. I tried restarting, deleting default mqtt.cfg, uninstalled and installed MQTT from paperUI again… Nothing!
It is unclear what exactly you have done and in what order so I recommend uninstalling the binding, removing the mqtt.cfg and /var/lib/openhab2/config/org/openhab/mqtt.config files and restarting OH. Then follow these instructions:
I deleted the mqtt enrtry from the Karaf database again, and it suddenly started to display some mqtt errors in the log. Than, after a restart it connected correctly! Great! Now on to the next problem!