If you read through this entire thread, you will find that the only reliable fix that people have found is opening the TV and moving or just spraying the ribbon cable ends. I did this over a year ago and still is working fine. Admittedly this is an extreme measure for some people, but there are YouTube videos that show how to do it. My original post is: https://www.lgwebos.com/topic/3520-popup-messages-wired-lan-cable-disconnected-wired-network-is-connected/?do=findComment&comment=24874
Read serveral of the posts that just preceed mine and you will see many other people had good results. The only downside is that you have to be willing to risk damaging your TV, but in my case, I was willing to pay for a replacement TV to get rid of the problem, so this solution avoided buying a new TV.