I figured it out. One of my Smart Power Outlets reset itself for some reason. When this happened, the Device Network ID (DNI) changed for that device. It use to be EBFC, and now it is C242. The other devices knew it was there and routing through it, but the HUB didn’t know what it was and was reporting it as Unknown Device (EBFC). I unplugged the Smart Power Outlet, waited 5 minutes, plugged it back in, and it immediately went into Pairing Mode. Paired it with the HUB. Unplugged the HUB and removed the batteries. Waited 30 minutes. Plugged the HUB back in, inserted the batteries. Everything is good now. No more Unknown Device.
Does anyone know what would cause a device to change it’s DNI? This is very odd to me, and I’ve never had this happen before.