The DNS Health Test is shows the following warnings:
"The Secondary DNS server <IPAddress> is taking <time> to respond"
"The Secondary DNS server <IPAddress> failed with the following error. A connection attempt failed"
The Domain Controllers only have a Primary DNS server set for each NIC.
The test will continue to fail due to no Secondary DNS server IP Address configured for the DC's NIC. Modify the test to not check for the Secondary DNS server: