r6900, amber port light stays on even with port connected to tv and working

If its an ethernet port, its implying a 10/100mbps connection and not gigabit. 

Which is pretty standard for tv's. Most tv's don't have a gigabit connection, just 10/100mbps.

they don't need faster speeds than that as even a 4k broadcast only takes 25-40mbps. 

 

https://kb.netgear.com/23991/What-are-the-LEDs-and-ports-on-the-front-panel-of-my-Nighthawk-router-called