Apex domains cannot have CNAME records.
Question and response
Question
dig produktion.corp.enbw.com. NS
Answer
produktion.corp.enbw.com. 5 NS ns-1014.awsdns-62.net.
produktion.corp.enbw.com. 5 NS ns-211.awsdns-26.com.
produktion.corp.enbw.com. 5 NS ns-1931.awsdns-49.co.uk.
produktion.corp.enbw.com. 5 NS ns-1259.awsdns-29.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0