Apex domains cannot have CNAME records.
Question and response
Question
dig ipv6.lon01.syrahost.com. NS
Answer
ipv6.lon01.syrahost.com. 5 NS names1.ds.network.
ipv6.lon01.syrahost.com. 5 NS names2.ds.network.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0