The issue continues.

Unity Editor Version : 2019.4.28f1

Code :

ILeaderboard mLeaderBoard = Social.CreateLeaderboard();
mLeaderBoard.id = "leaderboardID";
mLeaderBoard.userScope = UserScope.Global;
mLeaderBoard.timeScope = TimeScope.AllTime;
mLeaderBoard.range = new Range(1, 30);

mLeaderBoard.LoadScores(result =>
{
if (result)
{
Debug.Log("Scores Length : " + mLeaderBoard.scores.Length); //Output : "Scores Length : 30"

List<string> userIDs = new List<string>();

for (int i = 0; i < mLeaderBoard.scores.Length; i++)
userIDs.Add(mLeaderBoard.scores[i].userID);

Debug.Log("UserIDs Count : " + userIDs.Count); //Output : "UserIDs Count : 30"
Debug.Log("UserID[0] : " + userIDs[0]); //Output : "UserID[0] : 162334654......"
Debug.Log("Player ID : " + Social.localUser.id); //Output : "Player ID : T:_9953b2d1m32......"

Social.LoadUsers(userIDs.ToArray(), (users) =>
{
Debug.Log("Users Length : " + users.Length); //Output : "Users Length : 0"
});
}
});

Although 30 Scores are returned, users information is not loaded. Social.LoadUsers function returns user array of length is 0.
It also gives the following error in XCode Console :

"GKPlayer: _loadPlayersForIdentifiers: - Failed to get profiles for Player IDs due to error: Error Domain=GKErrorDomain Code=8 "The requested operation could not be completed because the player is invalid." UserInfo={GKServerStatusCode=5005, NSLocalizedDescription=The requested operation could not be completed because the player is invalid., NSUnderlyingError=0x600000e11d70 {Error Domain=GKServerErrorDomain Code=5005 "status = 5005, NO SUCH PLAYER ID" UserInfo={GKServerStatusCode=5005, NSLocalizedFailureReason=status = 5005, NO SUCH PLAYER ID}}} "

I noticed here that the userID of the users on the leaderboard are not similar to Social.localuser.id. Different types. So I tried using Social.LoadUsers function with Social.localuser.id

Code:

List<string> userIDs = new List<string>();
userIDs.Add(Social.localUser.id);
Social.LoadUsers(userIDs.ToArray(), (users) =>
{
Debug.Log("Users Length : " + users.Length); //Output : "Users Length : 0"
});

But the result is the same. Social.LoadUsers function returns 0. But this time it didn't give any error in XCode Console.