[REQUIRED] Please fill in the following fields:

• Unity editor version: 2021年3月19日f1
• Firebase Unity SDK version: 10.3.0
• Source you installed the SDK: .unitypackage
• Problematic Firebase Component: Auth (Auth, Database, etc.)
• Other Firebase Components in use: Firestore, Analytics, CloudFunctions, Crashlytics
• Additional SDKs you are using: Facebook, AdMob
• Platform you are using the Unity editor on: Mac
• Platform you are targeting: iOS
• Scripting Runtime: IL2CPP
• Pre-built SDK from the website or open-source from this repo: prebuilt

[REQUIRED] Please describe the issue here:

I have updated Firebase to 11.4.0 months ago, everything worked fine until I tried running a standalone Windows build, had the good and old crash on start that is usually fixed by installing redistributables (check box on steamworks).
Knowing that 10.3.0 worked before I rolled back to 10.3.0 and things started working again.

All good until I tried to build for iOS, everything works correctly but for some reason the userId I get from firebase auth is different from what I get with 11.4.0 or what I used to get with 10.3.0. No code has changed on my side, it was just a version change. And to confirm it was the version, if I build with 11.x.0 I get the correct userId, but with 10.x.0 I get a new one.

Example code below:

On 11.x.0 newUser.UserId is cuzPiRT7QFgPZ2COBC0hbMGlvGU2
On 10.x.0 newUser.UserId is Y7Bj2PKv3maCmrPIMdTGd1YluUC3

Steps to reproduce:

Upgrade to 11.x.0
Fetch the userId
Downgrade to 10.x.0
Fetch the userId
userId is now different on 10.x.0

Relevant Code:

using UnityEngine;
using UnityEngine.SocialPlatforms.GameCenter;
public class GameCenterLogin {
	public static void Initialize() {
		GameCenterPlatform.ShowDefaultAchievementCompletionBanner(true);
		Social.localUser.Authenticate((bool success) => {
			if (success) SignInWithGameCenterAsync();
			else CloudLogin.OnFail();
		});
	}
	private static void SignInWithGameCenterAsync() {
		Firebase.Auth.FirebaseAuth auth = Firebase.Auth.FirebaseAuth.DefaultInstance;
		var credentialTask = Firebase.Auth.GameCenterAuthProvider.GetCredentialAsync();
		credentialTask.ContinueWith(cTask => {
			if (!cTask.IsCompleted || cTask.Exception != null || cTask.IsCanceled || cTask.IsFaulted) {
				Debug.Log("GCL credentialTask failed" + cTask.Exception.Message);
				CloudLogin.OnFail();
				return null;
			}
			var credential = cTask.Result;
			auth.SignInWithCredentialAsync(credential).ContinueWith(task => {
				if (task.IsCanceled || task.IsFaulted) {
					CloudLogin.OnFail();
					Debug.Log("GCL SignInWithCredentialAsync failed");
					return;
				}
				Firebase.Auth.FirebaseUser newUser = task.Result;
				CloudLogin.OnSuccess(newUser.DisplayName, newUser.UserId);
			});
			return credential;
		});
	}
	public static void OpenRankingUI() {
		Social.ShowLeaderboardUI();
	}
}