Facebook-sdk-for-unity: iOS: "Open this page in Facebook?" popup blocks login

Checklist

• [ ] I've updated to the latest released version of the SDK
  I downgraded to 7.19.2 because 7.21.1 was causing the app to crash on startup.
• [x] I've searched for existing GitHub issues
• [x] I've looked for existing answers on Stack Overflow, the Facebook Developer Community Forum and the Facebook Developers Group
• [x] I've read the Code of Conduct
• [x] This issue is not security related and can safely be disclosed publicly on GitHub

Environment

Describe your dev environment here, giving as many details as possible. If you have them, make sure to include:

• Unity Editor Version: 2019.3.0f3
• Unity SDK Version: 7.19.2
• Installation Platform & Verison: iOS version 13.5.1

Goals

Log into the game with Facebook.

Expected Results

The user is able to go through the login flow.

Actual Results

When running on an iPhone X, after calling FB.LogInWithReadPermissions and tapping "Continue" on the prompt, this screen comes up:

I'm not able to dismiss the "Open this page in Facebook?" popup, either by tapping "Cancel," "Open," or outside of the popup. The browser's top-left "Cancel" button works fine. Uninstalling and reinstalling the Facebook app fixed the issue for one run, but for subsequent runs, the issue returned.

This issue doesn't occur on an iPad Pro with iOS 13.5.1 or an iPad Air with iOS 12.4.7.

Another issue is that the keyboard isn't opened for text input in websites opened by the game - for example, by the Google Sign-in SDK. For some reason, this is fixed on the iPhone after uninstalling the Facebook app (and broken after reinstalling it)! However, this issue occurs on the iPad regardless of if the Facebook app is installed or not.

Steps to Reproduce

Edit: successfully reproduced:

1. Create a new Unity project and add SDK 7.19.2
2. Remove Play Services Resolver
3. Add Google Sign-In 1.0.4 without Parse and Play Services Resolver
4. Add External Dependency Manager 1.2.156 and add registry when prompted
5. Create a script on the camera and in Start, call FB.Init, then FB.LoginWithReadPermissions
6. Build for iOS with the device SDK
7. In the Podfile, change GoogleSignIn version to < 5.0.0
8. Run on an iPhone X with iOS 13.5.1 and the Facebook app (don't have access to any other iPhones)

Code Samples & Details

Link to reproduction.

Code:

public class TestScript : MonoBehaviour
{
    // Start is called before the first frame update
    void Start()
    {
        FB.Init(() => {
            FB.LogInWithReadPermissions(
                new List<string>() { "public_profile", "email", "user_friends", "user_posts" }, 
                loginResult => {

                }
            );
        });
    }

    // Update is called once per frame
    void Update()
    {

    }
}

Output:

2020-07-13 10:45:05.042142-0400 FacebookSandbox[11263:4698992] Built from '2019.3/staging' branch, Version '2019.3.0f3 (6c9e2bfd6f81)', Build type 'Release', Scripting Backend 'il2cpp'
-> applicationDidFinishLaunching()
2020-07-13 10:45:05.608167-0400 FacebookSandbox[11263:4698992] FBSDKLog: starting with Graph API v2.4, GET requests for /1184331378431008/model_asset should contain an explicit "fields" parameter
-> applicationDidBecomeActive()
GfxDevice: creating device client; threaded=1
Initializing Metal device caps: Apple A11 GPU
Initialize engine version: 2019.3.0f3 (6c9e2bfd6f81)
2020-07-13 10:45:05.630826-0400 FacebookSandbox[11263:4699191] [] tcp_input [C2.1:3] flags=[R] seq=4067646681, ack=0, win=0 state=CLOSED rcv_nxt=4067646681, snd_una=952914416
2020-07-13 10:45:05.631434-0400 FacebookSandbox[11263:4699191] [] tcp_input [C2.1:3] flags=[R] seq=4067646681, ack=0, win=0 state=CLOSED rcv_nxt=4067646681, snd_una=952914416
2020-07-13 10:45:05.633674-0400 FacebookSandbox[11263:4699191] [] tcp_input [C1.1:3] flags=[R] seq=1622058020, ack=0, win=0 state=CLOSED rcv_nxt=1622058020, snd_una=3506061178
2020-07-13 10:45:05.633732-0400 FacebookSandbox[11263:4699191] [] tcp_input [C1.1:3] flags=[R] seq=1622058020, ack=0, win=0 state=CLOSED rcv_nxt=1622058020, snd_una=3506061178
2020-07-13 10:45:06.342714-0400 FacebookSandbox[11263:4698992] Unbalanced calls to begin/end appearance transitions for <SplashScreenController: 0x15dd05b40>.
2020-07-13 10:45:06.359559-0400 FacebookSandbox[11263:4699195] [] tcp_input [C3.1:3] flags=[R] seq=2077033276, ack=0, win=0 state=CLOSED rcv_nxt=2077033276, snd_una=616266740
2020-07-13 10:45:06.361976-0400 FacebookSandbox[11263:4699195] [] tcp_input [C3.1:3] flags=[R] seq=2077033276, ack=0, win=0 state=CLOSED rcv_nxt=2077033276, snd_una=616266740
2020-07-13 10:45:06.365490-0400 FacebookSandbox[11263:4699195] [] tcp_input [C6.1:3] flags=[R] seq=2625008296, ack=0, win=0 state=CLOSED rcv_nxt=2625008296, snd_una=1507674903
2020-07-13 10:45:06.365527-0400 FacebookSandbox[11263:4699195] [] tcp_input [C6.1:3] flags=[R] seq=2625008296, ack=0, win=0 state=CLOSED rcv_nxt=2625008296, snd_una=1507674903
2020-07-13 10:45:06.901348-0400 FacebookSandbox[11263:4699192] [] tcp_input [C5.1:3] flags=[R] seq=1080860623, ack=0, win=0 state=CLOSED rcv_nxt=1080860623, snd_una=3380130027
2020-07-13 10:45:06.905260-0400 FacebookSandbox[11263:4699192] [] tcp_input [C5.1:3] flags=[R] seq=1080860623, ack=0, win=0 state=CLOSED rcv_nxt=1080860623, snd_una=3380130027
UnloadTime: 0.302667 ms
Using Facebook Unity SDK v7.19.2 with FBiOSSDK/6.5.2
Facebook.Unity.CompiledFacebookLoader:Start()

(Filename: ./Runtime/Export/Debug/Debug.bindings.h Line: 35)

-> applicationWillResignActive()
-> applicationDidBecomeActive()