MQTT binding some times drop connection to broker.
OH restart helps.
I use OH 1.8.1. May be this bugs fixed in v.1.8.3 mqtt binding?
2016-08-14 22:30:32.097 [ERROR] [.c.mqttv3.internal.ClientState] - openhab: Timed out as no activity, keepAlive=60,000 lastOutboundActivity=1,471,202,986,105 lastInboundActivity=1,471,203,017,929 2016-08-14 22:30:47.317 [ERROR] [o.o.b.m.i.MqttMessagePublisher] - Error publishing... org.eclipse.paho.client.mqttv3.MqttException: Client is not connected