When I did a dirty install of this firmware, the DoT preset server list was missing from the webUI, so I entered the Quad9 servers manually. Been using this since the 1/11 release date.
Yesterday when the latest AC86U firmware dropped, I did a clean install of this firmware on the AX86U. The DoT preset server list was present, although the entries for Quad9 are simply Quad9 1 and Quad9 2.
However, selecting the DoT preset servers for Quad9 installed a weird/corrupt looking address... something like 2008:24::ef:. I backed out to the top and tried again with expected results:
DoT1 184.108.40.206 dns.quad9.net
DoT2 220.127.116.11 dns.quad9.net
Now you know!
2620:fe::fe is their IPV6 address. Was it possibly this?