I have 5 LG TVs but only my largest and newest 65SJ8000 model has this exact "Wired Lan cable disconnected / Wired network is connected" issue. I have taken the TV back to factory settings with "no" change in its habits.
Very disappointed that it seems to be a common issue and even more disappointed that no one has been able to find a solution. Since this TV is only 2 years old LG has let us all down.