Above line says a host with IP 192.168.1.1 is acting as a DHCP server for your LAN segment.
Above says its handing out its own IP 192.168.1.1 to the clients to be used for resolving DNS.
Preferred is below (also check the links inside):
And about clients having Pi-hole + another for DNS:
Sounds like a firewall issue on either the host itself or some router safety mechanism blocking: