I've been having this issue with my iPhone 6 Plus 128GB. Prior to iOS 8.1.1., Spotlight Search would stop returning apps in search results. iOS 8.1.1 seems to have made the problem worse. Now Spotlight Search stops returning ANY results. I just get a blank screen. Powering down and restarting the iPhone and then waiting several minutes for re-indexiing will temporarily fix the issue. But I'll start getting blank search results again if I wait an hour. I really hope this gets fixed in the next iOS update! I rely on Spotlight Search to quickly launch apps without having to scroll through pages of apps to find them.