Apex domains cannot have CNAME records.
Question and response
Question
dig f5clouddns.com. NS
Answer
f5clouddns.com. 5 NS ns2.f5clouddns.com.
f5clouddns.com. 5 NS ns1.f5clouddns.com.
Authority
The response has no authority records.
Additional
ns1.f5clouddns.com. 5 A 107.162.234.197
ns2.f5clouddns.com. 5 A 107.162.176.221
ns1.f5clouddns.com. 5 AAAA 2604:e180:1071:0:0:0:3:1
ns2.f5clouddns.com. 5 AAAA 2604:e180:1071:0:0:ffff:6ba2:b0dd
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0