I have the same problem. It is very annoying.
I have wireless disconnected and only ethernet connected.
Already switched cable to other ports in the router, switched physical cable, and the problem remains.
I wonder if this is a hardware fault (ethernet board on tv) or is this a webos (software) problem?
LG, please resolve this as it seems that more people have the same issue.
We purchased and LG UHD SmartTV with WebOS at end of July 2018. The following messages continuously alternate re. the Wired Ethernet connection whenever the LAN cable is plugged in, i.e. "Wired network is connected" followed immediately by "Wired Lan cable disconnected".
However, the router is stable and there is a trouble-free, continous Wi-fi connnection to the same Smart TV. There are also no failures for other devices connected via a Wired Ethernet connection to the same router.
Dear LG ... is this a WebOS software issue or is it a SmartTV network card issue ? If this is not resolved very quickly we will dump this TV and buy SAMSUNG instead.