Pi-Hole not blocking ads

Sounds like the Asus router is pushing two DNS servers to the clients via DHCP:

If want to know for sure, install nmap on Pi-hole:

sudo apt install nmap

And do a DHCP discovery targeting the "<ASUS_ROUTER_IP_ADDRESS>":

sudo nmap -sU -p67 --script dhcp-discover <ASUS_ROUTER_IP_ADDRESS>