Guys, I had this problem on my LG 49UH770V. It was always hard wired to my router, never tested wireless. I constantly had the LAN disconnected and reconnected problem. This however stopped happening when I upgraded my old Ethernet cables (connected to my TV, Sky Q and PS4) to these: KabelDirekt 5m Cat6 Gigabit Ethernet Cable with Snagless RJ45 Connector (High-Speed and Reliable 1Gbps Internet Cord/Patch Cable with F/UTP Foil Shiel
This is the link, although the title has changed so I'm not sure if they are the exact same ones. https://www.amazon.co.uk/gp/product/B01FHZNXXI/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&th=1
Hope this helps.