XB7 - LAN Connection through Ethernet Ports on XB7 Dropping

have a XB7 since the release and it worked fine. Since a couple of days, XB7 is dropping connections randomly. Devices that directly connected via Ethernet are getting disconnected and dropping. Done everything (cable, reboot etc) and also exchanged the XB7 at Xfinity store. Still dropping connection. WiFi is still flawless