I upgraded one of my Echo Dot's to the new 3rd generation dot, and now I can't say within a room "Alexa turn off the lights" … "sorry, I did not find a device named lights". With the 2nd gen device it knows which echo is associated with a light in a room and just turns off the relative lights.
I have the new device associated in a group with the "light" that it is to control, but it doesn't work. In my other room with 2nd gen device it still works, so I know it is not an online glitch.
UPDATE: It was my error, I guess I was confused by the new "Preferred Speaker" option in the app and thought I had the Alexa linked to the room for room commands, but it was not. Working now.