I have an iOS app with WatchKit 1.0 support. Since Xcode 9.2, I received the following warning only for the included WatchKit application:
App Store Icon 1024x1024 required for iOS apps
But the required image already exists and has the correct size and format (PNG):

If I load my application in TestFlight, I get a similar warning in the dialog box and in the mail:
. WatchOS App Store 1024x1024px PNG. iTunes Connect -. . https://developer.apple.com/watchos/human-interface-guidelines/icons-and-images/home-screen-icons/.
App Store iOS . WatchKit.
?
: , , actool (/Applications/Xcode.app/Contents/Developer/usr/bin/actool), .car .xcassets. , App Store (: , , Xcode):
/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/AppIcon24x24@2x.png
/Users/clemens/Desktop/bugreport/AppIcon27.5x27.5@2x.png
/Users/clemens/Desktop/bugreport/AppIcon29x29@2x.png
/Users/clemens/Desktop/bugreport/AppIcon29x29@3x.png
/Users/clemens/Desktop/bugreport/AppIcon40x40@2x.png
/Users/clemens/Desktop/bugreport/AppIcon44x44@2x.png
/Users/clemens/Desktop/bugreport/AppIcon86x86@2x.png
/Users/clemens/Desktop/bugreport/AppIcon98x98@2x.png
/Users/clemens/Desktop/bugreport/Assets.car
/Users/clemens/Desktop/bugreport/Info.plist