Google Play Game Services Sign In Problem

Hi,

A beta tester said to me that every time he restarts the scene(with a button) he must sign in again. According to the github play game services project: "If the user has already signed into the game in the past, this process will be silent and the user will not have to interact with any dialogs." But this unfortunately doesn't work for us.

The sign in script is on the same scene as the game is:

 using UnityEngine;
 using System.Collections;
 using GooglePlayGames;
 using GooglePlayGames.BasicApi;
 using UnityEngine.SocialPlatforms;
 
 public class PlayeServices : MonoBehaviour {
 
     void Awake () {
         PlayGamesPlatform.Activate();
     }
 
     void Start () {
         Social.localUser.Authenticate((bool success) => {
             if(success){
                 Debug.Log("Successfully logged in");
             }
             else{
                 Debug.Log("Login failed");
             }
         });
     }
 }

Can anyone help me?