If you're seeing installs reported for a mobile app engagement campaign, it's because people have uninstalled your app or are viewing the ad on a device that is different to the one they downloaded the app on (e.g. a second tablet or a new phone). If the device detects that the app is not currently installed, the ad will ask the user to re-install the app or install it for the first time on the new device. These installs are reported as engagement.

* Nguồn: Facebook