Cloud symbol next to apps
Solution 1:
Source:
These are offloaded apps, new for iOS 11. A cloud next to an icon means you enabled offloaded apps and this app was deleted, but the data was saved and you can re-download the app by tapping on it. When you tap the app, it begins to redownload to your device, as you've seen.
To change this behaviour, go to Settings -> iTunes & App Store and change the switch for Offload unused apps.