Since updating to iOS 11, I've lost the ability to surface apps from the swipe-down Spotlight search field. This was my preferred method of launching apps as it was quite a lot more convenient than swiping through endless pages of icons.
I found a couple of references (MacObserver, Reddit) pointing out that this behavior has been changed in iOS 11. Users are now forced to enable Search & Siri Suggestions for EACH app (found under Settings > Siri & Search)
If you do not do this, then the only way to surface an app via Spotlight is to type out the FULL APP NAME verbatim. Yes, that's C-a-l-c-u-l-a-t-o-r.
Not enough, apparently...
That last R — convenient!
Also, search does not yield the same result as past versions. Now, content from within the apps is also displayed. For example, if Evernote has its Siri function enabled, not only will the app itself show up in Spotlight, but also any notes inside Evernote that contain your search term. This is unwanted and potentially hazardous to privacy.
There seems to be no way to disable this or revert its behavior. I am posting this as a warning as well as a plea to any Apple engineers who might stumble onto this post. Apple, please fix this broken feature.