Can't resolve *.mil domains when using AirVPN DNS server

[nva 0]

I recently noticed that i can't visit any *.mil websites when I'm using AirVPN with Wireguard client for MacOS. Config file downloaded from Client page looks like this:
 

[Interface]
PrivateKey = ...
Address = ...
DNS = 10.128.0.1
MTU = 1320

[Peer]
...

dig command returned with SERVFAIL:
 

~ > dig @10.128.0.1 www.navy.mil

; <<>> DiG 9.10.6 <<>> @10.128.0.1 www.navy.mil
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 51388
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.navy.mil.			IN	A

;; Query time: 2554 msec
;; SERVER: 10.128.0.1#53(10.128.0.1)
;; WHEN:
;; MSG SIZE  rcvd: 41

But it works fine with if i choose Mullvad (also wireguard):

~ > dig www.navy.mil

; <<>> DiG 9.10.6 <<>> www.navy.mil
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17697
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;www.navy.mil.			IN	A

;; ANSWER SECTION:
www.navy.mil.		7138	IN	CNAME	www.navy.mil.edgekey.net.
www.navy.mil.edgekey.net. 300	IN	CNAME	e16312.dscb.akamaiedge.net.
e16312.dscb.akamaiedge.net. 20	IN	A	23.15.145.170

;; Query time: 597 msec
;; SERVER: 100.64.0.7#53(100.64.0.7)
;; WHEN:
;; MSG SIZE  rcvd: 132

On a semi-related note: my Opnsense router running Unbound in DNS-over-TLS forwarding mode to upstream DNS servers also got exactly same error: SERVFAIL or straight up timeout with dig command for *.mil domains. Upstream queries go through WAN and not any VPN tunnel. Turning DNSSEC on and off didn't change anything on my opnsense router. If i don't use DNS-over-TLS and just plain forwarding to UDP 53, no issue.

I don't know how relevant these two issues are, perhaps AirVPN also use Unbound? 

Once you find out what's wrong, can you drop some info so i can also fix my Opnsense settings?

Thank you!

[Staff 9969]

@nva

Hello!

Each VPN server runs its own DNS server. The authoritative server for the mentioned domain names either blocks a lot of DNS IP addresses (not only AirVPN ones, as you noticed) or is malfunctioning. In both cases you would get a SERVFAIL error message.

Kind regards