To fix the issue, you just need to register the apps again in your computer which will automatically add all missing apps to Start Menu, Taskbar and installed apps list. It seems a bug in the upgrade process of Fall Creators Update which makes the installed apps not working after the upgrade. The only way to access the apps is Store. So basically the apps exist in the machine but they don’t appear in Start Menu, Taskbar, Cortana search results and installed apps list. If the user tries to search for the apps in Store, it shows that the apps are already installed in the computer and the user is able to launch the apps using Store. If the user searches for the apps using Cortana search box, the apps don’t appear in the search result and Cortana suggests to install the apps from Windows Store. The apps also disappear from the installed apps list in Settings. If the apps shortcuts were pinned to Taskbar, they are also missing after the upgrade. After installing Fall Creators Update, many installed apps icons are missing from Start Menu.
