You get a generic Twixl Publisher icon in iTunes Connect after uploading the .ipa with Application Loader.
Twixl Publisher supports the iPhone X. But because of that, only the latest version of Xcode can be used.
- Install the latest version of Xcode (9.2 is the minimum release to support the iPhone X).
- Create a new build of your application
- Upload your app again with the Application Loader version that is included in that Xcode release