Pi Hole is not blocking ads

[deHakkelaar]

rdwebdesign, doesnt that fe80::1 IP show up in the debug log dhcp-discover output as an RDNSS?
If it does, I think you have to poke in the ZTE router > LAN > RA service settings.

Some hints for another ZTE model below (the bottom paragraph):

IPv6 DNS configuration on ZTE H6645P

I am not aware of any such requirement. If that would be the case, any Windows running on a network with IPv4 only connectivity would never be able to receive updates. When considering to disable IPv6, it would be crucial whether your ISP is providing you with a native dual stack, native IPv4 or native IPv6 connection. Obviously, disabling IPv6 is not an option in the latter case. Configuring a DHCPv6 DNS Server may not help. Most OSs won't use DHCPv6, but SLAAC, learning network details …