DNS_PROBE_FINISHED_NXDOMAIN error occurred when I set up two DNSs with the same ELB in your name .com.

DNS_PROBE_FINISHED_NXDOMAIN error occurred when configuring two DNSs with the same ELB in your name .com.

[Configuration]
The configuration is like setting the ACM on the ELB and hanging one EC2 under it.

DNS name for ELB:
elb Name - xxxxxxxxx.ap-northeast-1.elb.amazonaws.com

Route 53 is not used and
We set the DNS record with the following DNS name as com.

DNS record settings in .com
https://gyazo.com/7bb869f72e68a6952356f74a0789a4f9

The first release only runs a subdomain called sub1 and
sub1.example.com

I released the service and it was running without any problems.

Since it was running steadily, the next improvement is
We have decided to deploy services for specific users by dividing subdomains.

Therefore, after configuring the subdomain named sub2 with the name .com,

sub2.example.com

I released a service called

However, from then on,
for subdomains of sub2 DNS_PROBE_FINISHED_NXDOMAIN error has occurred.

At the same time, the above error is not for all users, but for some users (all users who have received previous inquiries tend to be Window users)
is the only one that has an error and not everyone can see it.

[Setting in com]

sub1.example.com CNAME3600elb Name - xxxxxxxxx.ap-northeast-1.elb.amazonaws.com
sub2.example.com CNAME3600elb Name - xxxxxxxxx.ap-northeast-1.elb.amazonaws.com

Therefore, I am troubled because I do not know the cause.

I tried various things and asked your name com.
Could you please let me know if you can find any information that can give me a hint?

dig CNAME sub2.example.com

; <>>DiG 9.8.3-P1<>CNAME sub2.example.com.
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<-opcode:QUERY, status: NOERROR, id:33436
;; flags:qrrdra;QUERY:1, ANSWER:1, AUTHORITY:0, ADDITIONAL:0

;; QUESTION SECTION:
;elb Name - xxxxxxxxx.ap-northeast-1.elb.amazonaws.com.INCNAME

;; ANSWER SECTION:
sub2.example.com.3599 INCNAME elb Name - xxxxxxxxx.ap-northeast-1.elb.amazonaws.com.

;; Query time—110 msec
;; SERVER: xxx.xxx.x.x#53 (xxx.xxx.x.x)
;; MSG SIZE rcvd—107

Thank you for your cooperation.

I don't want to be as responsive to end users as possible because it's for B2C.
Is there a possibility that this kind of thing will solve the problem?

Clear DNS Cache
http://www.errorcode-search.com/command/Windows10/admin-tool-command/ipconfig-flushdns.html