Try using a VPN to see if you can circumvent what ever is blocking access in your country/location. Other possible steps, temporarily try different DNS servers and disable any DNS filtering programs/apps you may be using.
AXE160000 with native IPV6, AIMesh, and pihole/unbound (two raspberry pi's): So I've been running this mismash system according to this Asus FAQ for quite some time:
However, things seem to have reverted to the "If your router firmware version < 3.0.0.4.386.45898" with newest firmware. As soon as I entered my pihole IPV4 addresses in the LAN/DHCP server section things calmed down (it takes a while). I use ::1 for the ipv6 box. Make sure that router advertisement is disabled in LAN/DHCP server. I'm wondering whether " Enable Router Advertisement" should also be turned off under the IPV6 section. I have the pihole actual fe80 addresses listed in the IPV6 DNS section. I still occasionally (less than once a day) get the ">1000 dns attempts" error on the piholes, but I think it mainly happens during a reboot (been doing a lot of reboots lately as I experiment), although it does imply a feedback loop (maybe the ipv6?). Anyway, things are much improved. Passes the " https://test-ipv6.com" test. Wife is happier.