OpenSprinkler dropping offline repeatedly

Further to this, it sort of works through the openHAB interface, even when it’s complaining about being offline. The interface doesn’t track the state perfectly, but I can toggle stations on and off. So communications between the openHAB host and the opensprinkler seem to be running, even though PaperUI and the openHAB log both confidently tell me that the opensprinkler is offline.