Got it. Sorry about that confusion. I didn't know dns would appear as a cors error.
Discussion
It normally shouldn’t. I suspect something is going on with your DNS responses being tampered with, maybe something like a corporate firewall?
I use unbound in recursive mode behind blocky. When an address gets blocked its supposed to return A 0.0.0.0. I don't know what happens on not found. Usually the 2s timeout occurs before unbound can return a not-found result.