b.regfish-ns.net has no CNAME records.
Question and response
Question
dig b.regfish-ns.net. NS
Answer
The response has no answer records.
Authority
regfish-ns.net. 4648 SOA a.regfish-ns.net. dns.regfish-ns.net. 1730187994 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0