I wired a new Rachio 3 this morning and this afternoon I saw one of my main valves leaking. Could this be something related to wiring at Rachio or completely unrelated?
You are looking at a anti-siphon device (aka backflow preventer), a passive device designed to stop contaminated irrigation water being sucked back into clean water supply. This device does not, by itself, contain a valve, nor is it possible to control it in any way from an irrigation controller.
Here (link) it is the website for the device. You may be able to find troubleshooting / maintenance instruction by contacting their support and/or searching youtube.