tv 4K thinks it's connected to ethernet

My Apple 4k TV keeps thinking it's connected to an ethernet cable, but it's not. When I restart, it will connect to wifi and everything works fine. After about 5 minutes, everything stops working. I check Network, Connection and it says Ethernet, even though there is no cable plugged in. I've checked the empty ethernet port and nothing appears damaged. I've reset router, updated tv 4K software, taken it back to factory settings, etc. Nothing seems to convince this little box that it's not connected to an ethernet cable! Any suggestions would be appreciated. Thanks.