Problems finding WatchKit App Store Icon

Question

I've got an iOS app with WatchKit 1.0 support. Since Xcode 9.2 I get the following warning only for the included WatchKit App:

A 1024x1024 app store icon is required for iOS apps

But the required image is already exists and has the correct size and format (PNG):

If I upload my app to TestFlight I get a similar warning in a dialog and per mail:

Missing App Store Icon - WatchOS Apps must include a 1024x1024px App Store Icon in PNG format. Without providing the icon in the Asset Catalog or via iTunes Connect, apps cannot be submitted for App Review or Beta App Review. Refer to https://developer.apple.com/watchos/human-interface-guidelines/icons-and-images/home-screen-icons/ for more information.

Adding an App Store image for iOS App works fine and gives no errors. This error only occurs for the WatchKit app.

How can I solve this issue?

EDIT: The error seems to be in the actool (/Applications/Xcode.app/Contents/Developer/usr/bin/actool) which creates the .car file from the .xcassets file. When I execute it with my assets, it ignores the App Store icon (Note: The parameters except file and folder names are copied from Xcode's compile log):

/Applications/Xcode.app/Contents/Developer/usr/bin/actool \
    --output-partial-info-plist Info.plist \
    --output-format human-readable-text --notices --warnings \
    --app-icon AppIcon --target-device watch --compress-pngs \ 
    --enable-on-demand-resources NO \
    --filter-for-device-model iPhone9,3 \
    --filter-for-device-os-version 11.2 \
    --sticker-pack-identifier-prefix com.myapp.watchkitapp.sticker-pack. \
    --minimum-deployment-target 9.0 --platform iphoneos \
    --product-type com.apple.product-type.application.watchapp \
    --compile . Images.xcassets

/* com.apple.actool.document.warnings */
/Users/clemens/Desktop/bugreport/Images.xcassets:./AppIcon.appiconset: warning: A 1024x1024 app store icon is required for iOS apps
/* com.apple.actool.compilation-results */
/Users/clemens/Desktop/bugreport/[email protected]
/Users/clemens/Desktop/bugreport/[email protected]
/Users/clemens/Desktop/bugreport/[email protected]
/Users/clemens/Desktop/bugreport/[email protected]
/Users/clemens/Desktop/bugreport/[email protected]
/Users/clemens/Desktop/bugreport/[email protected]
/Users/clemens/Desktop/bugreport/[email protected]
/Users/clemens/Desktop/bugreport/[email protected]
/Users/clemens/Desktop/bugreport/Assets.car
/Users/clemens/Desktop/bugreport/Info.plist

Answer 1

Of course, the image needs to be 1024x1024 and with no transparency, and I'm sure you already got that sorted out. But, that's not the issue in this case.

I know this will sound weird and unrelated, but I had the absolutely same issue on one of my projects and can confirm the fix works.
You must upgrade to at least WatchKit 2.0.