Thanks for looking into the issue. After adding the 48 pixels size icon also it is not showing the icon while installing the app. Please let us know if you need more information.
Are you using the ipa-app-store?If yes then it is expected that icon won't be visible in iTunes and at the time of installation as for high retina devices as for App Store icon 1024x1024 is applicable and this icon will be used by App Store to publish your app.
If your problem is something else then do let me know.
The icon is not displaying while installing the ad-hoc package app. Now we released the app(same code set) into Apple iStore and there is no icon issue with the distributed version(The app which is in iStore).