There is an auto decline if the person receiving the invitation is either in a game or in the game setup screen. Could you try setting up a game ensuring that the recipient of the invite is not in the game setup?
As I posted up above, if the recipient launches the app and just sits at the dashboard they can accept invites just fine. I have found a couple of things I need to address in the next release to make this easier and allow for people to accept invites from the setup screen if they haven’t started a game.