Hi tefica,
The first thing to check is to make sure sure the leaderboard ID in the leaderboard map in the project settings is exactly the same as the leaderboard ID you see in the Google developer console. If that’s set up correctly, does the logcat output show any information related to leaderboards? You’ll need to use a non-shipping build to see UE4’s log output, but it will print diagnostic messages for leaderboard operations. If we could see this log output, it would be very helpful.