Unable to resolve csboa.csb.gov.hk

Zero Trust 1.1.1.1
1 
dig csboa.csb.gov.hk @1.1.1.1

; <<>> DiG 9.10.6 <<>> csboa.csb.gov.hk @1.1.1.1
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 7412
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1452
;; QUESTION SECTION:
;csboa.csb.gov.hk.		IN	A

;; ANSWER SECTION:
csboa.csb.gov.hk.	101	IN	CNAME	csboa-csb.3dns.info.gov.hk.

;; Query time: 4003 msec
;; SERVER: 1.1.1.1#53(1.1.1.1)
;; WHEN: Wed Jul 18 11:41:42 BST 2018
;; MSG SIZE  rcvd: 79

dig csboa.csb.gov.hk @8.8.8.8

; <<>> DiG 9.10.6 <<>> csboa.csb.gov.hk @8.8.8.8
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42972
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;csboa.csb.gov.hk.		IN	A

;; ANSWER SECTION:
csboa.csb.gov.hk.	299	IN	CNAME	csboa-csb.3dns.info.gov.hk.
csboa-csb.3dns.info.gov.hk. 29	IN	A	202.128.254.58

;; Query time: 3334 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Wed Jul 18 11:41:29 BST 2018
;; MSG SIZE  rcvd: 95
2

Apparently, it is resolvable now.

dig csboa.csb.gov.hk @1.1.1.1

; <<>> DiG 9.10.6 <<>> csboa.csb.gov.hk @1.1.1.1
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 42030
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1452
;; QUESTION SECTION:
;csboa.csb.gov.hk.		IN	A

;; ANSWER SECTION:
csboa.csb.gov.hk.	300	IN	CNAME	csboa-csb.3dns.info.gov.hk.
csboa-csb.3dns.info.gov.hk. 1	IN	A	202.128.254.58

;; Query time: 703 msec
;; SERVER: 1.1.1.1#53(1.1.1.1)
;; WHEN: Wed Jul 18 13:12:27 BST 2018
;; MSG SIZE  rcvd: 95