I know it’s been more than a year, but this issue is still present. IPV6 can’t be disabled on google fiber routers, and you can’t set custom IPV6 DNS servers. This effectively means most modern devices are going to default to the IPV6 DNS and circumvent PiHole. I was pulling my hair trying to figure out why my phone was able to get through to “blocked” sites. This is some real BS from google. I’ve raised the issue to the support team and they’ve escalated it to a supervisor. I’ll post an update if they provide any solutions or workarounds.