I faced with a problem in Xcode 9 (works fine in Xcode 8 before). I can't upload tvOS build because of incorrect image asset for App Store icon. But App Store icons have exactly 1280x768 size and 3 layers. I was able to upload build to iTunes before with Xcode 8. But now I receive such error:
ERROR ITMS-90718: "Invalid Image Asset. The App Store Icon must only contain an image with size (1280pt × 768pt @1x). Refer to https://developer.apple.com/tvos/human-interface-guidelines/icons-and-images/app-icon for more information"
Do you happen to have also 2x version of your assets in the Xcode? I had this same issue than you and I was somehow presuming that I would need to provide also 2x version, but once I removed that and only have the 1x, the upload succeeded!