Why do I only see my router's IP address instead of individual devices in the Top Clients section and Query Log?

[un-zero]

When the router's DNS cannot be deactivated, even if you are using pi-hole's DHCP, you still get in effect two DNS servers (the router, which then directs DNS requests to pi-hole, and the pi-hole itself). To fix this:

@un-zero

Additional trick: to prevent clients from appearing as ' _gateway ' on the pi-hole, change the router DNS to e.g. 192.168.200.200 (or some other non-existent address on your local network). That way, the pi-hole's DNS is the only working DNS on your network, and all clients now reach to it directly (and thus, are identified correctly by pi-hole with their Mac and IP addresses).