Ads not blocked on some clients

[deHakkelaar]

Maybe ads are leaking through the IPv6 DNS server(s) configured on the Win client:

netsh interface ipv4 show dnsservers

netsh interface ipv6 show dnsservers

Or the DNS answers coming from the DNS server(s) might be malformed/protected by some AV software:

Literally no ads being blocked

That Windows machine you are using wouldn't run a virus scanner like AVAST? AVAST offers a feature called RealSite that will inject additional DNS queries to a "trusted" DNS server (run by AVAST) in case something goes wrong with normal DNS resolution, see Hilfe: Windows löst Hostname auch ohne PiHole auf? - #26 by Chris80 (though German, it also contains a short solution description in English).