Firstly, apologies for the dumb question but networking is not my area of expertise.

My current set-up is VDSL using the ISP supplied HG659 as it was intended, a 1 box system to take care of routing and Wifi. I have a Shield TV connected via Ethernet, I prefer to use Ethernet as I have a 4K TV and subscribe to Netflix premium offering for 4K content. I also occasionally use the Sheild TV to chromecast from a mobile device however to do so I have to disconnect the Ethernet cable and connect the Shield TV to the Wifi network. Whenever the Shield TV is connected to Ethernet I can't even see it to cast to it but as soon as I disconnect the Ethernet cable it is there and work fine.

Is there something I need to change in the router settings to enable casting to an Ethernet connected device?

Thanks