github.com's NS records say nsone.net and AWS are authoritative for it. However, all of the authoritative nsone.net servers are answering queries for github.com with no A records. The AWS DNS servers are responding with A records as normal.

Try for yourself with `dig github.com NS`, and then `dig github.com @dns1.p08.nsone.net.` (or any of the other nsone.net servers).

githubstatus.com reports all is operational.