i dont think its a pihole-only problem but i hope i will get some help here too.
-I've set up a pi hole
-made it the default dns for the router
-blacklisted google.com (as an example).
Now it starts to get strange: cant reach google.com with chrome on android (2phones tested). CANT PING google.com from the windows client, but i CAN reach google.com with firefox on windows and macOS. (but its listed in the pihole log as blocked)
same behavior if i setup the pihole by hand for the winodws client.
One client at a time - do some web browsing while tailing the Pi-Hole log. See if you see traffic from that client that matches the sites you browse. If you don't, that client is not sending any (or some) of its DNS traffic through Pi-Hole.
After you did this, did you renew the DHCP lease on all the clients?
Also note that the domains google.com and www.google.com are different domains. If you have google.com blocked but are browsing www.google.com, you will get to the site.