Same for me. Since yesterday. Connection is excellent. The controller is working in the menu, I can select and start the games but if I'm in the game the input is gone.
Restarted CCU, Wifi and Stadia but no change.
I played in the morning and in the evening nothing worked as expected.
Same for me. Stadia controller works great with Stadia menus, however in-game the controller doesn't appear to work at all. I tried multiple games, same result. I'm using the Stadia controller that was delivered in December 2019 with Chromecast Ultra. Of that helps at all. 🙂
This is happening to me since the very beginning.
From time to time the controller stops working (only in the game!) but Stadia menus keep doing well. Don't know what is going on, I've try different wifis, ethernet, reseting, everything... is super annoying.