Flutter App IOS Release Build Error: Missing Required Icon File

I built the IOS release build and created the Product archive on Xcode. But when I try to validate the archive I get this error:

flutter doctor -v output:

    [✓] Flutter (Channel beta, v0.8.2, on Mac OS X 10.13.6 17G65, locale en-US)
    • Flutter version 0.8.2 at /Users/westworld/development/flutter
    • Framework revision 5ab9e70727 (2 weeks ago), 2018-09-07 12:33:05 -0700
    • Engine revision 58a1894a1c
    • Dart version 2.1.0-dev.3.1.flutter-760a9690c2

[✓] Android toolchain - develop for Android devices (Android SDK 28.0.2)
    • Android SDK at /Users/westworld/Library/Android/sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-28, build-tools 28.0.2
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)
    • All Android licenses accepted.

[✓] iOS toolchain - develop for iOS devices (Xcode 10.0)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 10.0, Build version 10A255
    • ios-deploy 1.9.2
    • CocoaPods version 1.5.3

[✓] Android Studio (version 3.1)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 28.0.1
    • Dart plugin version 173.4700
    • Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)

[✓] VS Code (version 1.27.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 2.18.0

[!] Connected devices
    ! No devices available

! Doctor found issues in 1 category.

Xcode Deployment Target is 10.0.

Also, the Assets.xcassets folder exists in the ios/Runner folder:

But I don't see it in the Xcode folder structure:

So, for the App Icons Source I cannot choose the AppIcon folder:

Not sure if I asked this clearly, but have anyone encountered the same problem?

I think your file system has gotten out of sync somehow. If you right click on Assets.xcassets in Android Studio and then click Reveal in Finder what does that show? Does it actually exist in your project folder? If it is then you might just need to drag it into Xcode, and delete the current AppIcon file.

Before you do any of that you might also try running flutter clean and File->Sync with File System in Android Studio.