ns1.yandexcloud.net has no CNAME records.
Question and response
Question
dig ns1.yandexcloud.net. NS
Answer
The response has no answer records.
Authority
yandexcloud.net. 300 SOA ns3.yandex.ru. sysadmin.yandex.ru. 2048138030 900 600 3600000 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0