apollo.ns.cloudflare.com has no CNAME records.
Question and response
Question
dig apollo.ns.cloudflare.com. NS
Answer
The response has no answer records.
Authority
cloudflare.com. 149 SOA ns3.cloudflare.com. dns.cloudflare.com. 2397350190 10000 2400 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0