The reason that the app does not appear is that it is most likely a 'foreground' app- an app that is running and made to stay that way.

Depending upon the device and the memory capacity, along with how much memory the app uses, the system may let it run or shut it down.

Something that might be possible, depending on the device, is called 'Pinning' the app.

On some devices, this will force it to remain in the foreground and avoid the OS from shutting it down.