The torrent of traffic I'm receiving has caused my AWS bill to spike from $9 to $148, all of the increase due to bandwidth charges.
To remediate, I'm replacing ns-azure with ns-hetzner. The previous release replaced ns-aws with ns-ovh.
ns-hetzner has both IPv4 and IPv6 addresses. It appears that Google's 8.8.8.8 DNS service favors IPv6-based nameservers.