Previously I used an E900 router with stock firmware (simple configuration) but I recently installed DD-WRT and the official Pi-Hole configuration guide and other post but I can not make it work quite well, it does not show the total of connected clients.
The only clients that count towards the 3 clients shown in the dashboard are those which have made DNS requests via Pi-hole. Just having the client using the DHCP server does not qualify as being a client of the DNS server.