How did you set the IP? Is it the upstream DNS of the router itself?
Because your router advertises itself und two public DNS servers via DHCP to its clients
* Received 340 bytes from eth0:192.168.1.1
Offered IP address: 192.168.1.10
Server IP address: N/A
Relay-agent IP address: N/A
BOOTP server: (empty)
BOOTP file: (empty)
DHCP options:
Message type: DHCPOFFER (2)
server-identifier: 192.168.1.1
lease-time: 86400 ( 1d )
netmask: 255.255.255.0
router: 192.168.1.1
dns-server: 192.168.1.1
dns-server: 1.1.1.1
dns-server: 8.8.8.8
renewal-time: 43200 ( 12h )
rebinding-time: 75600 ( 21h )
The clients will then choose one of those DNS servers as they like to answer their DNS requests.
Set PI-hole as the only DNS server distributed via DHCP (and dis/reconnect the clients from the network to pick-up the new settings).