The icon of the app is grayed out or not visible
In some rare occasions the iOS installer can encounter a problem when installing or updating an app. We recommend you open the Settings app and navigate to the section called "iTunes & App Store" and make sure you are signed in with your Apple ID. Then reboot your device: press and hold the power/sleep button until a power off message appears then confirm it; once your device finished shutting down, press the power/sleep to turn it on. After rebooting try install or updating the app once again. If this does not help, try installing the app using iTunes.