1.1.1.1 is well known (based on the announcement from cloudflare anyway) to have tons of random traffic. That's part of the reason it wasn't implemented by others as a valid address for anything. Could the fact that they're simply allowing traffic at that address cause additional stress on AT&T's network?
I ask because I don't know. I figure any traffic headed that direction would go anyway it just wouldn't get routed very far with no valid destination.