But if I go to Game Centre, I can still browse through the game list and see the Leaderboard data, and the other 2 games were working ok, so I wasn't too worry about that.
However sometime last week, it changed. As shown below, although it says 67 games at the beginning, after tapped on the "Games" icon at the bottom, it shows "No Leaderboard or Achievements". What the...
A few days ago, it gets worse. As below, it's showing "Not Available" and wouldn't show anything. Note that the phone doesn't have SIM card (hence the "SOS only" message) but it's always connected to WiFi, so definitely no network connectivity issue.
And even other games installed on the same iPhone 5 also showing "No Items" for Leaderboard.
Start searching on the net and found a few others also experiencing similar issue, and got their problem resolved by reset the phone settings.
At the same time, my iPad 2 also have a funny issue with the Game Centre - no matter how I try, it also shows as "sandbox" in Game Centre.
As the iPad 2 is not as important as the iPhone 5, I use it as guinea pig and tried the "Reset All Settings" fix - it works! Other than losing the WiFi password and backend images, no other data were lost - which is one of my concern. Forgot to capture screen shot on the iPad 2 but I did capture the iPhone 5 one, as below, just select the first "Reset All Settings" and wait for it to restart.
After that, all the game Leaderboard/Achievements returned in the Game Centre!
And the Leaderboards for all 4 games all worked now!