Apex domains cannot have CNAME records.
Question and response
Question
dig bitrix24.net. NS
Answer
bitrix24.net. 4 NS ns-633.awsdns-15.net.
bitrix24.net. 4 NS ns-1986.awsdns-56.co.uk.
bitrix24.net. 4 NS ns-366.awsdns-45.com.
bitrix24.net. 4 NS ns-1181.awsdns-19.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0