Now in iOS 11 you must in Settings > Siri & Search enable "Search & Siri Suggestions" for every app you want to show up in Spotlight Search results when only typing a partial name for an app. If you don't do that, apps will still show up in Spotlight Search, but you must type the *entire* name of the app. But, by enabling "Search & Siri Suggestions" you'll also see data from within all the apps in search results. I don't want that, as I only use Spotlight Search to launch apps, and I don't want iOS indexing data from all my apps regardless.
I'm hoping this is a bug and not a feature, as it didn't work that way in iOS 10. Either way, it's frustrating, as again that's all I use Spotlight Search for.
I suggest you report it here https://www.apple.com/feedback/ and hopefully it will get fixed.