looks to me like… a classic “evil brother” symptom: (/var/lib/openhab2/config/org/openhab/mqtt.config in your case… the evil brother of /etc/openhab2/services/mqtt.cfg 
)
add the following line as the first line in your mqtt.cfg
pid:org.openhab.mqtt
Ref: Troubleshooting section of MQTT Binding (v1.11) Getting Started 101