Actually it is syncing. You just cant be using the two devices at the same time. Only one of them has working syncing when doing it this way. I'm guessing I copied over some identifier that needs to be unique. But At least I figured out it's possible to sign in and that it's not a "server error".
My guess is that the opera app generates a identifier for the device and sends it to the server when signing in through the app. On newer android versions that identifier doesn't look like the server expects it to and the server just throws back a generic error message.
Of-course if you log one device out you log them both out. 