nslookup for public domains to Active Directory domain controller DNS server times-out *and* still succeeds

The problem:

Lately I've noticed Chrome on my desktop stalling when it loads a new website, saying it's resolving the domain-name. Eventually it resolved, but it feels like DNS requests take up to 5 seconds to succeed, which isn't right.

The Set-up:

• Windows Server 2012 R2 Active Directory domain controller.

  • IPv4 address: 172.16.1.10 (name: server.my.ad.domain)
  • Windows DNS Server is configured to use only Google's 8.8.8.8 and 8.8.4.4 as the only Forwarders.
    • It is also configured to use Root hints if no forwarders are available.
  • dcdiag passes all tests.

• Windows 10 desktop computer, member of the domain.

  • Name: desktop.my.ad.domain
  • Network settings:
    • Bluetooth PAN: Disabled ("Not connected")
    • Ethernet: Connected (Domain network profile)
      • DHCP enabled.
      • Using only 172.16.1.10 as its DNS server.

nslookup Output:

I ran this from my desktop - I was surprised to see timeout errors but for the name to resolve eventually without needing a second invocation of nslookup:

C:\>nslookup stackoverflow.com
Server:  server.my.ad.domain
Address:  172.16.1.10

DNS request timed out.
    timeout was 2 seconds.
Non-authoritative answer:
DNS request timed out.
    timeout was 2 seconds.
Name:    stackoverflow.com
Addresses:  151.101.65.69
          151.101.1.69
          151.101.129.69
          151.101.193.69

I can't seem to reliably reproduce the issue - even after running ipconfig /flushdns on both my desktop and the server, and removing the cached items from the Windows DNS Server's cache.

I tried again just now with nslookup and set debug and I got this:

> openra.net
Server:  server.my.ad.domain
Address:  172.16.1.10

------------
Got answer:
    HEADER:
        opcode = QUERY, id = 16, rcode = NXDOMAIN
        header flags:  response, auth. answer, want recursion, recursion avail.
        questions = 1,  answers = 0,  authority records = 1,  additional = 0

    QUESTIONS:
        openra.net.my.ad.domain, type = A, class = IN
    AUTHORITY RECORDS:
    ->  my.ad.domain
        ttl = 3600 (1 hour)
        primary name server = server.my.ad.domain
        responsible mail addr = hostmaster.my.ad.domain
        serial  = 8384
        refresh = 900 (15 mins)
        retry   = 600 (10 mins)
        expire  = 86400 (1 day)
        default TTL = 3600 (1 hour)

------------
------------
Got answer:
    HEADER:
        opcode = QUERY, id = 17, rcode = NXDOMAIN
        header flags:  response, auth. answer, want recursion, recursion avail.
        questions = 1,  answers = 0,  authority records = 1,  additional = 0

    QUESTIONS:
        openra.net.my.ad.domain, type = AAAA, class = IN
    AUTHORITY RECORDS:
    ->  my.ad.domain
        ttl = 3600 (1 hour)
        primary name server = server.my.ad.domain
        responsible mail addr = hostmaster.my.ad.domain
        serial  = 8384
        refresh = 900 (15 mins)
        retry   = 600 (10 mins)
        expire  = 86400 (1 day)
        default TTL = 3600 (1 hour)

------------
------------
Got answer:
    HEADER:
        opcode = QUERY, id = 18, rcode = NXDOMAIN
        header flags:  response, want recursion, recursion avail.
        questions = 1,  answers = 0,  authority records = 1,  additional = 0

    QUESTIONS:
        openra.net.ad.domain, type = A, class = IN
    AUTHORITY RECORDS:
    ->  ad.domain
        ttl = 298 (4 mins 58 secs)
        primary name server = ns1.bdm.microsoftonline.com
        responsible mail addr = azuredns-hostmaster.microsoft.com
        serial  = 1
        refresh = 3600 (1 hour)
        retry   = 300 (5 mins)
        expire  = 2419200 (28 days)
        default TTL = 300 (5 mins)

------------
------------
Got answer:
    HEADER:
        opcode = QUERY, id = 19, rcode = NXDOMAIN
        header flags:  response, want recursion, recursion avail.
        questions = 1,  answers = 0,  authority records = 1,  additional = 0

    QUESTIONS:
        openra.net.ad.domain, type = AAAA, class = IN
    AUTHORITY RECORDS:
    ->  ad.domain
        ttl = 298 (4 mins 58 secs)
        primary name server = ns1.bdm.microsoftonline.com
        responsible mail addr = azuredns-hostmaster.microsoft.com
        serial  = 1
        refresh = 3600 (1 hour)
        retry   = 300 (5 mins)
        expire  = 2419200 (28 days)
        default TTL = 300 (5 mins)

------------
------------
Got answer:
    HEADER:
        opcode = QUERY, id = 20, rcode = NOERROR
        header flags:  response, want recursion, recursion avail.
        questions = 1,  answers = 1,  authority records = 0,  additional = 0

    QUESTIONS:
        openra.net, type = A, class = IN
    ANSWERS:
    ->  openra.net
        internet address = 194.63.248.52
        ttl = 3599 (59 mins 59 secs)

------------
Non-authoritative answer:
DNS request timed out.
    timeout was 2 seconds.
timeout (2 secs)
Name:    openra.net
Address:  194.63.248.52

>

Unfortunately it still doesn't tell me exactly what timed-out...