EX6400 problems with connectivity and throughput

I've recently installed an EX6400 into my home network for both extending my wifi range and the ethernet connection to an older Samsung SmartTV without a wireless connection. My main router is an Xfinity Arris TG1682G operating in both 2.4 and 5GHz ranges and separated by different SSID's at the main router. I am having a twofold problem. First, my Google ChromeCast attached to the TV will not connect to either the 2.4 or 5G extended networks when I turn the TV on. However, if I turn the extender off and then on again, the ChromeCast is able to find and connect to the router. At the same time, the ethernet connection to the TV stays live and has no connectivity issues when the set is turned on. Secondly, all of my other devices will give an "Internet not available" message until the extender is power cycled, then all is well until the connections go dormant, then I have to go through the power down cycle again (if I'm away for an hour or more). Now the Arris TG1682G does not see the EX6400 as an Extender but I have set it up as a static IP within the modem domain. All firmware is up to date. I am ready just to return it and go with an entirely different set-up, either MoCA or powerline so this my last ditch effort.