ATV (3rd & 4th gen) wake up from sleep without wired internet connection
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I have encountered the same issue with two 3rd gen and 1 4th gen ATV, where the device has lost it's wired internet connection, when it comes back from sleep. In all cases the ATV is connected to an Airport Express (latest version) and the connection only get's restored once I reboot my cable modem (to which the AE is connected).
Disconnecting the ethernet cable and reconnecting it (on both the ATV or AE end) has the ATV NOT re-discover the internet connection, and the same issue also occurs when using WiFi connection between ATV and AE.