Thanks for the reply.
The router's DHCP pool is configured from 192.168.1.11 to 192.168.1.254. The Pi is using 192.168.1.2 so no device can claim that ip.
The output of nslookup pi.hole is:
pi@raspberry:~ $ nslookup pi.hole
Server: 9.9.9.10
Address: 9.9.9.10#53
** server can't find pi.hole: NXDOMAIN