What type of router do you have. And if you set the router back to use your normal DNS does everything work correctly?
On the router/WAP are you using DHCP to give the client machines an IP address? And can you configure a DNS server on the DHCP screens to that you are sending the DNS server address directly to the clients?
Also, check and see if you can manually configure a DNS server on the client, and put in the IP address of the Pi-hole, this will check if a direct connection will work.
And lastly, check on the router for something called DNS Rebind, this will block DNS responses from a server on the local network if enabled.
Sorry I maxed out my replies for a first time account. My router is a netgear 7800 and when I turned auto DNS on everything worked perfectly. DHCP is active on the router. Here is a pic of the only place in the router I can chance DNS. I also couldn't find a way to send the DNS server addy directly to the clients. I found a couple of post that alluded to the fact you can't run apihole on some netgear routers without flashing a different OS.
You can always write a private message to one of us asking for an extension of this limit. It is there to prevent spammers from flooding our forum, as we are all free timers and we don't have the resources to moderate this platform for 24h. Don't laugh but there are people who think that we are doing supporting this forum badly and should set up a moderator (which is getting payed somehow) instead of applying such limits. I hope you understand our point of view.
Well, I think you might run into a situation many users have seen lately, i.e. if you set a DNS server inside your network, it does not work anymore. Often, these routers are heavily restricted and apply crazy filtering of all kinds.
I have seen you wrote:
Would it be an option for you to switch to the Pi-hole internal DHCP server (see Settings page?). I implemented for exactly this purpose, when the router's DHCP server cannot be used for whatever reason. If you would like to stay with your router's DHCP server (for whatever reason), could you try to use the Pi-hoel DHCP server only temporarily to see if it would fix the problem you are seeing?
Remember to disable the DHCP server of your router after activating the Pi-hole one and reconnect your devices to your network (like WiFi Off/On toggle).