I've been having this same issue, very annoying. I have been using Stadia since launch and never ran into this issue until this week.
I typically access Stadia through Chrome on my laptop. I went on a work trip, and paid extra for the enhanced wifi at the hotel to play. Clicked on the game I wanted to play, and got the loading circle which eventually gives me the same message (reopen the game to play). But that doesn't work. Tried other games, same issue. I gave up. Then the next day while at the airport I tried again. This time it loaded fine.
I get home, and now run into this issue about ever other time I try to open any game. The only solution I've found is to close out the game I'm trying to play (say Rage 2), then open Destiny 2 (which sometimes works, sometimes doesn't), then close Destiny and open Rage 2. This happens with every game, so it's not specific to one title. Sometimes it takes several attempts.
Never had this issue until now. I was fully into Stadia, but this loading issue is turning me off. I assume it's some sort of glitch where it thinks a game is still open or something, and won't allow it to load? If this continues, I'll probably cancel my pro membership and stick with consoles. First world problems I know. But if I'm paying for a game and service, and some glitch isn't letting me access my content, it puts me off to continue using Stadia.
