Our house has many devices (Chromecasts, XBOXs, Smart Tvs, tablets, etc).  Many times when we try to cast to a TV the device is not listed.  When i set up the router (C2600) i created two SSIDs one for 2.4GHZ and one for 5GHZ.  Unfortunately, my tablet may be using the 2.4GHZ band while my TV (Chromecast) is using the 5GHZ.  When I switched my tablet to the other band the device is then seen and casting is possible.

To avoid this I first changed the name of the 5GHZ SSID.  For some reason some of the devices could still find and use the old SSID on 5GHZ.  Next I completely turned off the 5GHZ wireless radio using the TP-LINK GUI.  Now on my laptops and on some of the devices I can see the 2.4 GHZ SSID and both of the 5GHZ SSIDs.  I can also connect to both and access the internet and other wireless actions.  

I am at a loss.  I rebooted the router after these changes were made many time, I even unplugged and plugged the router back in.  All SSIDs are available and allow connection and internet access.....any ideas of there?