Game Center save game data to iCloud

We are trying to implement saving and fetching data to and from iCloud, but it have some problems.

MacOS: 15.3

Here is what I do:

1. Enable Game Center and iCloud capbility in Signing & Capabilities, pick iCloud Documents, create and select a Container.

2. Sample code:

void SaveDataToCloud( const void* buffer, unsigned int datasize, const char* name )
{
    if(!GKLocalPlayer.localPlayer.authenticated) return;

    NSData* data = [ NSData dataWithBytes:databuffer length:datasize];
    NSString* filename = [ NSString stringWithUTF8String:name ];
    [[GKLocalPlayer localPlayer] saveGameData:data withName:filename completionHandler:^(GKSavedGame * _Nullable savedGame, NSError * _Nullable){
        if (error != nil)
        {
            NSLog( @"SaveDataToCloud error:%@", [ error localizedDescription ] );
        }
    }];
}

void FetchCloudSavedGameData()
{
    if ( !GKLocalPlayer.localPlayer.authenticated ) return;
    [ [ GKLocalPlayer localPlayer ]  fetchSavedGamesWithCompletionHandler:^(NSArray<GKSavedGame *> * _Nullable savedGames, NSError * _Nullable error) {
			if ( error == nil )
			{
				for ( GKSavedGame *item in savedGames )
				{
					[ item loadDataWithCompletionHandler:^(NSData * _Nullable data, NSError * _Nullable error) {
						if ( error == nil )
						{
                    //handle data
						}
						else
						{
							NSLog( @"FetchCloudSavedGameData failed to load iCloud file: %@, error:%@", item.name, [ error localizedDescription ] );
						}
					} ];
				}
			}
			else
			{
				NSLog( @"FetchCloudSavedGameData error:%@", [ error localizedDescription ] );
			}
		} ];
}

Both saveGameData and fetchSavedGamesWithCompletionHandler are not reporting any error, when debugging, saveGameData completionHandler got a nil error, and can get a valid "savedGame", but when try to rebot the game and use "fetchSavedGamesWithCompletionHandler" to fetch data, we got nothing, no error reported, and the savedGames got a 0 length.

From this page https://developer.apple.com/forums/thread/718541?answerId=825596022#825596022 we try to wait 30sec after authenticated , then try fetchSavedGamesWithCompletionHandler, still got the same error.

Checked:

1. Game Center and iCloud are enabled and login with the same account.
2. iCloud have enough space to save.

So what's wrong with it.