Pihole allowing ads through

Expected Behaviour:

[Pihole should be blocking most ads. Hardware - PiZeroW, Router - Netgear - C6250-100NAS]

Actual Behaviour:

[Pihole appears to be working fine. It's receiving traffic and appears to be blocking. However, ads are still appearing everywhere. I've tried slickdeals and other test sites. I've specified PiHole as my only DNS (both on IPv4 and 6). I checked in ipconfig /all for verification. Blocklists have been added. I changed so Pihole is the DHCP Server as well and disabled it on my router. I just don't know where else to check.]

Debug Token:

[ https://tricorder.pi-hole.net/1xuxfic5k9]

From a client where you you see ads, and that you believe should be connected to the Pi-Hole for DNS, from the command prompt or terminal on that client (and not via ssh or Putty to the Pi), what is the output of

nslookup pi.hole

DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
DNS request timed out.
timeout was 2 seconds.
*** Request to UnKnown timed-out

What's the IP of the DNS server that this was trying to contact?

99% of the time you'll find that you have additional IPv6 DNS servers that clients use from the routers RA data.

Are your clients using Pi-hole and only Pi-hole IP addresses as their DNS servers? Can you disable IPv6 to verify if your clients are truly using Pi-hole and not other DNS servers?

the IP is the IPv6 address of the pihole. server: unknown

Then that client is unable to talk to Pi-hole. Can you do nslookup for any other domains and see what DNS server IP is being used?

I tried both from the same client/different domains and different client/same domain & different domain. For same client/different domains, it list the DNS server IP as the IPv6 address of the pihole, but times out a couple of times before giving me the address of whatever domain I'm trying to reach. Out of curiosity, I tried a different client and the pihole appears to be working on that client fine (DNS server address is the IPv4 of the pihole & blocking ads). So I'm not sure why it isn't working on the first client.

At least you have eliminated Pi-hole as the problem.