Apex domains cannot have CNAME records.
Question and response
Question
dig yjs-cdn.com. NS
Answer
yjs-cdn.com. 5 NS ns1.yjs-cdn.com.
yjs-cdn.com. 5 NS ns2.yjs-cdn.com.
Authority
The response has no authority records.
Additional
ns1.yjs-cdn.com. 5 A 180.76.198.250
ns1.yjs-cdn.com. 5 A 180.76.199.216
ns2.yjs-cdn.com. 5 A 180.76.198.250
ns2.yjs-cdn.com. 5 A 180.76.199.216
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0