I have been reporting this from the beginning, but until now nobody paid attention 😞 so I will try again.
I experienced this on any PC I played until now - something about 8 to 10 machines, 4 different Internet provider with different technologies and three different Stadia accounts (now that GRID is a pro game it’s more easy to test with any account). I also observed other gamers in the race with the same issue. So that they do not report here, does not mean the issue is inexistant. At least I can tell you some more observation on when this happens. For me it seems to happen after a package lost - a normal issue on stadia, but sometimes it is like the game doesn’t forward the inputs of one of the keys any more. As I showed you in some videos, the input arrives at the game (there are some graphic evidences) but the action is not forwarded to the gameplay.
Finally I found out, how to recover control. First you have to turn completely in the direction that still works (without touching any other key) and then you press the key that doesn’t respond for some time (only that key) and you will recover control. You can imagine, that this only works at quite low speed, other wise you spin. When the acceleration doesn’t respond you will have to stop completely, press the brake, press the accelerator key and you can go on. This method seems to work most of the time, but you can forget the race your in. Quite annoying.   Here you can find my old post with the videos. If you need some more information, please ask https://forums.codemasters.com/topic/44268-grid-on-stadia-feedback-thread-for-stadia-players/?do=findComment&comment=488326

So please stop ignoring me with this issue 🙂