I just received a new Stadia controller and after running through the setup steps I was able to wirelessly connect it to Stadia on Chrome. Then after starting multiple games, I was unable to use the controller to play the games.
Actually it seems like the controller isn't responsive in the main menu either. It works fine when I plug it in, but it is unresponsive after linking it to the browser. I don't see any errors or anything after pairing, but the controller seems to buzz to indicate that it paired successfully and it doesn't buzz again if I attempt to enter the pairing code a second time.
have found that, if I connect to a different game device, like Chromecast to laptop, or laptop to Chromebook, I have to start all over again with the setup. Maybe the whole plugging in thing will do that. Try pushing and holding the Stadia button through two vibrations. Then, you may be able to enter the device code again. Either that, or you can do a factory reset. I think you just push capture and Assistant button until it vibrates.