Errors Launching Flutter app in iOS Simulator

I am experiencing issues when launching a Flutter app on iOS simulator. The issue seems to be relating to localhost connectivity or such, judging by the below error output, but I am unable to find how to fix it.

I am running MacOS Catalina version 10.15.6 (19G73). iOS simulator version Version 11.6 (921.9.1). VSCode is my IDE.

The app launches and runs fine on the Android simulator counterpart.

Below is the error output from VSCode Terminal:

Launching lib/main.dart on iPhone SE (2nd generation) in debug mode...
Running Xcode build...                                                  
 └─Compiling, linking and signing...                         6.7s
Xcode build done.                                           16.7s
Connecting to the VM Service is taking longer than expected...
Still attempting to connect to the VM Service...
If you do NOT see the Flutter application running, it might have crashed. The device logs (e.g. from adb or XCode) might have more details.
If you do see the Flutter application running on the device, try re-running with --host-vmservice-port to use a specific port known to be available.
Exception attempting to connect to the VM Service: SocketException: OS Error: Connection refused, errno = 61, address = 127.0.0.1, port = 51838
This was attempt #50. Will retry in 0:00:01.600000.
Exception attempting to connect to the VM Service: SocketException: OS Error: Connection refused, errno = 61, address = 127.0.0.1, port = 51970
This was attempt #100. Will retry in 0:00:01.600000.
Exception attempting to connect to the VM Service: SocketException: OS Error: Connection refused, errno = 61, address = 127.0.0.1, port = 52119
This was attempt #150. Will retry in 0:00:01.600000.
Exception attempting to connect to the VM Service: SocketException: OS Error: Connection refused, errno = 61, address = 127.0.0.1, port = 52347
This was attempt #200. Will retry in 0:00:01.600000.
^C%

I had the same issue because of Firebase. I fixed my issue by inverting 2 lines in my AppDelegate.swift file:

FirebaseApp.configure() // Should be first
GeneratedPluginRegistrant.register(with: self) // Should be second

My non working file was this one

import UIKit
import Flutter
import Firebase

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self) // <- Don't do this
    FirebaseApp.configure()   // <- Don't do this
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

And my working file is:

import UIKit
import Flutter
import Firebase

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    FirebaseApp.configure()   // <- Do this
    GeneratedPluginRegistrant.register(with: self) // <- Do this
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}