The “higher level DNS” should not be changed in settings.py unless you are using a DNS service like Unblockus. Otherwise leave it be (set at 8.8.8.8, google’ public DNS.)
Also make sure your ATV itself is manually set to the same DNS as the computer running Plex Media Server.
I had the same problem and tried institute11 & sander1’s suggestion, which worked once, but now it isn’t working. I get the ‘trailers unavailable’ message after a long time trying to connect.
Additionally, after changing the DNS, I can’t access movies/connect to iTunes.
I am positive I have the right DNS by the way. It hasn’t changed in the 10 or so hours since it worked earlier.