Cannot change IP Subnet

Hi Bucking_Horn.

Thanks for your reply it was very informative.
I shall start looking somewhere else for the rogue ip address.
In the mean time here are the respones to your questions.

I set the ip address from the interface file. NetworkManager has been disabled and masked.

Interface file:

# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source /etc/network/interfaces.d/*

#auto eth0
##allow-hotplug eth0
#iface eth0 inet static
#        address 172.16.1.17/24
#        netmask 255.255.255.0
#        network 172.16.1.0
#        broadcast 172.16.1.255
#        gateway 172.16.1.1
#        dns-nameservers 172.16.1.17

auto eth0
#allow-hotplug eth0
iface eth0 inet static
        address 192.168.0.117/24
        netmask 255.255.255.0
        network 192.168.0.0
        broadcast 192.168.0.255
        gateway 192.168.0.1
        dns-nameservers 192.168.0.1

allow-hotplug wlan0
iface wlan0 inet static
    hostapd /etc/hostapd/wlan0-hostapd.conf
    address 10.42.0.10
    netmask 255.255.255.0
    network 10.42.0.0
    broadcast 10.42.0.255

output from ifconfig:

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.0.117  netmask 255.255.255.0  broadcast 192.168.0.255
        ether 2c:cf:67:19:9d:14  txqueuelen 1000  (Ethernet)
        RX packets 2202  bytes 143650 (140.2 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 5148  bytes 515624 (503.5 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 106  

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 114  bytes 8699 (8.4 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 114  bytes 8699 (8.4 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

wlan0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.42.0.10  netmask 255.255.255.0  broadcast 10.42.0.255
        ether 2c:cf:67:19:9d:15  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 25  bytes 3455 (3.3 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Here is the output from: pihole-FTL dhcp-discover

Scanning all your interfaces for DHCP servers
Timeout: 10 seconds

* Received 300 bytes from wlan0:10.42.0.10
  Offered IP address: 10.42.0.29
  Server IP address: 10.42.0.10
  Relay-agent IP address: N/A
  BOOTP server: (empty)
  BOOTP file: (empty)
  DHCP options:
   Message type: DHCPOFFER (2)
   server-identifier: 10.42.0.10
   lease-time: 259200 ( 3d )
   renewal-time: 129600 ( 1d 12h )
   rebinding-time: 226800 ( 2d 15h )
   netmask: 255.255.255.0
   broadcast: 10.42.0.255
   router: 10.42.0.10
   ntp-server: 192.168.0.1
   dns-server: 192.168.0.117
   --- end of options ---

DHCP packets received on interface eth0: 0
DHCP packets received on interface wlan0: 1

Here is my resolv.conf before pihole -d:

nameserver 9.9.9.9
#nameserver 192.168.0.1

I can't upload the debug.log as I don't have outward bound internet connectivity on the RPI configured for 192.168.0.x. so I've attached it to a reply email. Please let me know if there is some other method you would like me to use.