Any idea

Any idea why one is using 192.x.x.x and the other 10.x.x.x IP address?

I am using the router as a DHCP Server and have it configured to start at 192.168.1.2 and end at 192.168.1.254

I have no idea where the 10.x.x.x is coming from and why it is showing under attached devices at that address IP.