Apple TV looses connection overnight

My Apple TV always looses connection to the media library on the Mac Mini overnight. I enable sharing of the library, and the library appears on the Apple TV. Next morning, I cannot access the library anymore. I need to disable and re-enable sharing, all fine. After a few hours, connection is lost again. This happens constantly every day.

Setup: my Apple TV is 3rd generation, it connects to a Mac Mini (late 2012) via Powerline, i.e. the Apple TV is on the ground floor, the Mac Mini on the first floor. So the connection is: Apple TV -> Ethernet cable -> Router -> Ethernet cable -> Devolo Powerline device -> powerline -> Devolo Powerline device -> WLAN -> Mac Mini.

Anyone has any idea what might be the problem?