Apple just released the 2nd GM seed. See https://developer.apple.com/app-store-connect/whats-new/?id=09162019a
This causes builds uploaded with the first seed to fail:
You can now submit apps built with Xcode 11 GM seed 2 (11A420a) using the iOS 13 SDK and watchOS 6 SDK to the App Store. Apps built with Xcode 11 GM seed (11A419c) can no longer be uploaded to App Store Connect.
Error log from ci:
[01:06:07]: [Transporter Error Output]: ERROR ITMS-90534: "Invalid Toolchain. Your app was built with an unsupported version of Xcode or SDK. If you plan to submit this build to the App Store, make sure you are using the GM version of Xcode 9 and the SDK for iOS 11, tvOS 11, watchOS 4, or macOS 10.13 or later. If you are using an Xcode beta version to test your app, make sure you are using the latest supported version. For more information about supported beta versions, view the TestFlight Release Notes (https://developer.apple.com/testflight/release-notes/)." [01:06:07]: Transporter transfer failed.