There are no serviceable parts inside; the circuit diagram is subject to an NDA with Sigma. A warranty return or WD repair is your only option.
Before you return the device, try using it for a few days as a stand alone device with an attached USB drive and disconnected from the network. That at least will eliminate computer errors.
Think I’ve found the problem; it’s network related. My ISP has changed some settings, and the WD TV is unable to resolve DNS. Its sollution seems to be a spontaneous reboot in an effort to «solve» the problem. I unhooked my Ethernet cable, and it hasn’t been rebooting since then.