I had the same issue with 2 apps. Went to updates and scrolled through update history and turns out those two had started the update but didn't complete - they corrupted. I hit update again and they restored.
Happened to me a couple of days ago with my calendar app Fantastical 2. That icon appeared where its icon had been. Nothing happened when I tapped on it, and I couldn't delete it either (no X appeared on it). If I went to the App Store and went to updates there was no icon available to download or open.I finally solved it by doing a hard reset on the phone. When it had rebooted the app was back and everything worked normally. Checking updates again showed that the app had just been updated that day. So I agree with imjohnl that it has something to do with an update that didn't complete properly.
Actually, this happened to me regularly. None of the fixes above helped me. I used to know why it happened but I have forgotten. But I lived with it I think from one of the IOS 7 updates until IOS 8.1.3 or 8.1.4. I had a way to fix it. As you do this, note where each section was (3rd section down, etc). Trust me, it will help if you do not know more than one language. Go to settings>General>Language &Region>IPhone Language. Pick a language you are comfortable with (I used Japanese the firstt time and had to get Apple to walk me thru fixing it as nothing looked right. Now I stick to French as I studied that in school.). After you choose, it sets up the iPhone for that language. The icons will appear as they should. Now go back and do the same thing again, re choosing the language as English. You should be good to go. Until the next time you reboot your iPhone. Hth