My guess is this is just incompetence and not intentionally made to block CloudFlare.

I have one of those routers, and I couldn't use 1.1.1.1 because it was routing to an internal interface on the router. I confirmed this with ping, I was getting microsecond response times from 1.1.1.1.

Under the new firmware, 1.1.1.1 is just dead. So it's probably still connected to the local interface, and nothing is listening.