Facebook SDK 7.2.1 Unity Login Crash on device iOS9, not in editor

Everything is working perfectly inside unity editor, but when I build for iOS and test on device I get this error everytime I try to login to facebook:

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'can't start iterating in the middle of an iteration'

Here's the code I'm using inside Unity:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine.UI;
 using Facebook.Unity;
 
 public class NewFbLogin : MonoBehaviour 
 {
     public Button fbLoginBtn;
 
     public void FbLogin()
     {
         var perms = new List<string>(){"public_profile", "email", "user_friends"};
         FB.LogInWithReadPermissions(perms, AuthCallback);
     }
 
     private void AuthCallback (ILoginResult result) 
     {
         if (FB.IsLoggedIn) 
         {
             // AccessToken class will have session details
             var aToken = Facebook.Unity.AccessToken.CurrentAccessToken;
             // Print current access token's User ID
             Debug.Log(aToken.UserId);
             // Print current access token's granted permissions
             foreach (string perm in aToken.Permissions) 
             {
                 Debug.Log(perm);
             }
 
             fbLoginBtn.gameObject.SetActive(false);
         } else {
             Debug.Log("User cancelled login");
         }
     }
 }

Am I missing something?

Thanks for your help!