Hi @DanSchaper
I did some more digging and I think I've opened up a can of worms here.
First, the IPv6 issue
When I'm using the IPv6 DNS servers from DNS.watch, both the tests at http://ipv6-test.com/ and http://test-ipv6.com/ fail.
If I swap them for the IPv6 DNS servers from UncensoredDNS.org, the test at http://ipv6-test.com/ fails but the test at http://test-ipv6.com/ passes.
When using OpenDNS' IPv6 servers, both tests succeed... Hence I started testing each resolver manually because I didn't know what to think of it. Doing so, I also found out that that digwebinterface.com does not support testing IPv6 DNS resolvers (nice one...) and neither does Test DNS server records online (query A, AAAA, CNAME, MX, PTR, SPF, SRV, NS, TXT, or all available). However, KLOTH.NET - DIG - DNS lookup - find IP address does support testing IPv4 and IPv6 DNS resolvers so I used that to test DNS.watch, UncensoredDNS and OpenDNS.
Using Kloth.net, I was able to confirm that all three IPv6 DNS servers properly respond to a dig command, so why is http://ipv6-test.com/ and/or http://test-ipv6.com/ failing when I use DNS.watch (or UncensoredDNS.org) but passes when using OpenDNS? It doesn't make sense to me...
But now, IPv4 is somewhat broken as well..
While trying our different the different online DNS resolver test tools, I found out that my Pi-hole (while using the IPv4 address) is marked as dead by some tools, while other tools are able to resolve using it just fine. Here's a breakdown of each tool:
digwebinterface.com: Says my Pi-hole is NOT resolving DNS queries (NOK)
DNS Benchmark by Steve Gibson: Says my Pi-hole is NOT resolving DNS queries (NOK)
kloth.net: Says my Pi-hole is resolving DNS queries (OK)
manytools.org: Says my Pi-hole is resolving DNS queries (OK)
https://network-tools.com/nslook/: Says my Pi-hole is resolving DNS queries (OK)
https://www.subnetonline.com/pages/network-tools/online-dig.php: Says my Pi-hole is resolving DNS queries (OK)
Why the inconestenties in these results? I checked each tool to see if it was functioning properly by substituting my Pi-hole's IP by Google's DNS (8.8.8.8) and all tools provide a consistent OK/Yes while doing so....
At this point, I'm doubting if it's just easier to do a reinstall of the entire machine instead of troubleshooting this any further, unless you want to get to the bottem to this for future reference? The issue also persists when using the FTL-DNS beta / development branch. Here's the latest pihole -d output in case it changes anything: http://termbin.com/ielh
Thank you!
Kind regards