Prime31 Gamecenter Crash when triggering method

So after a lot of digging around and two days of solid learning and research, I have the answer.

I'm posting the code here so that anyone else who has a problem of not being able to turn off the Achievement Unlocked banner after it's been unlocked, here's the solution that worked for me. Hope that it saves you time!

In-game, when an achievement's parameters are met, I fire off the following:

 GameCentreGameManager.ReportAchievement("MIFOS_AC1_0"); //ID on iTunesConnect

I then have a script called "GameCentreGameManager.cs" that handles the event listener and methods...... (note that I'm not including all other code that's irrelevant)

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using Prime31;
 
 public class GameCentreGameManager : MonoBehaviour {
     
     #if UNITY_IPHONE
     public static string playerName;
     public static long playerHighScoreGC;
     public long _score;
     public static bool idFound;
     public static List<GameCenterAchievement> _achievements;
     
 //    Initialise Game Centre
     void Awake () 
     {
         GameCenterBinding.isGameCenterAvailable();    
     }
     
     void Start()
     {
         if (GameCenterBinding.isGameCenterAvailable() )
         {            
             GameCenterBinding.authenticateLocalPlayer(); //Must Have
             GameCenterBinding.showCompletionBannerForAchievements(); //Display banners on Achievement Unlocks...
         }    
         
         //Listener
         GameCenterManager.achievementsLoaded += achievementStatus =>
         {
             _achievements = achievementStatus;
         };    
     }
     
     
 //    Update the GC Leaderboard with new achievement. 
 //     The leaderboard will determine if the score is higher than what's already been previously posted and will only post a new high score automatically, thereby stopping the achievement banner from reappearing if subsequent repeats of achievement parameters are fulfilled.
     
     public static void ReportAchievement(string id)
     {        
         if (_achievements !=null)
         {
             foreach (GameCenterAchievement i in _achievements)
             {        
                 idFound = false; 
                 //search for achievement id in the list
                 if (!idFound) 
                 {
                 
                     if ( i.identifier == id)
                     {
                         Debug.Log ("Achievement already unlocked "+i.identifier);
                         idFound = true;
                         break;
                     }
                 }
             }
         }
             
            if (_achievements == null || !idFound) //First achievemeent ever to be unlocked or achievement id not in the list of unlocked achievements
         {
             Debug.Log("Unlocked Achievement: "+id);
                 GameCenterBinding.reportAchievement( id, 100 );
         }
     }    
     
     #endif
 }

I've done some rigorous testing of the above, including if whilst the game is open, and the player logs out of GameCentre via the GameCentre app, my game will automatically prompt for a user to sign in. When they do, the code above continues to function correctly for the new player, with relevant achievements unlocked etc and banner behaviour working correctly.

Also note, that for reference, I do have a Listener script that has the following.

 //Update the achievements when an achievement is successfully logged to GameCentre...
 void reportAchievementFinished( string identifier )
     {
         Debug.Log( "reportAchievementFinished: " + identifier );
         //Update the list on completion of the successful achievement....
         GameCenterBinding.getAchievements();
     }
 
 // When the player logs out and a new one logs in...
 void playerDataLoaded( List<GameCenterPlayer> players )
     {
         Debug.Log( "playerDataLoaded" );
         GameCenterBinding.getAchievements();
     }
 

As mentioned above, I've been testing it for an hour now with different and new Sandbox Users and haven't had any hiccups. Of course, my experience in C# and events is very limited, so if you see an issue with what I've done above, please let me know.

Thanks to those who helped out.

Cheers