I did all of the same things that everyone has done>Customer Service +2hrs>Chat +2hrs no change almost gave up...even checked Wifi connections (did not have any effect). Verified that I could have 3 max devices connected and even checked the 20 Wifi devices.
I did not realize that each device that is connected is counted against the 3 units...went back to my previously connected units and completely disconnected (even did an Uninstall of the TV app). And also went as far as disconnecting/unistall all of the remaining Xfinity apps (TV, TV-Go, Remote, WiFi and Connect). It worked I was able to connect my new iPad Air.
Solution/Conclusion: It seems that the system/server retains the latest connections and you have 'disconnect' from the system. If you have as many devices as I do 2-phones, 3-tablets, laptop and desktop, and want to change which unit is connected, you have disconnect one or more of you devices, before you'll be able to connect another unit.
This should be the responsibly of the TV app developer to inform the Customer Service people, they do have alot on their plate.
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