We have an app on iTunes (https://itunes.apple.com/us/app/pigame-free/id944503459). We have been getting reports that the achievements/leaderboards aren’t working. When the leaderboards/achievements buttons are pressed they open this page instead of displaying the correct stuff. It worked before we submitted to Apple. We’re using Unity’s Social API.
If your absolutely 100% sure that your code is not at fault here then the only thing you should do is report it to either Unity or Apple(this one could take a while), whoever is causing that site to open.
Maybe you forgot to turn off sandbox in iTunesconnect