Apex domains cannot have CNAME records.
Question and response
Question
dig ip-185.83.49.6.reverse.ymlp.net. NS
Answer
ip-185.83.49.6.reverse.ymlp.net. 5 NS ns2.afternic.com.
ip-185.83.49.6.reverse.ymlp.net. 5 NS ns1.afternic.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0