Base LAN address changes when Starlink looses satellite connection

I have a Starlink connection with the router in bypass mode. I am using a Nighthawk as DNS and DHCP server for the network. I have a requirement of a LAN base address of 192.168.100.x with a couple of fixed IP address devices.

My problem is whenever the router looses connection to the gateway (Starlink looses satellite contact) the base IP address for my LAN changes to 192.168.1.x or 10.1.1.x and my network is broken. How do I prevent the Nighthawk from doing that? I have used old routers that keep the base address unchanged when internet connection is lost. It seems this address change is a "feature" in newer routers.

Thanks for any help!