I have a problem when I developed my website with Google+ sign-in:
I did step by step that the doc told me but I always failed at step4:
https://developers.google.com/+/web/
The question is old but I faced this issue recently.
In my case, it was because I specified the URI parameter prompt to none. I guess Google doesn't like that if the user has never been logged to your platform before.
Whenever I changed that to consent or totally removed it, it worked great.