NightHawk M1 IP Passthrough Gateway

I've been using the Nighthawk M1 in IP Passthrough mode for a few months with DHCP turned off and it's Default Gateway set to 192.168.1.1 (factory default). It is connected to my Synology Router (RT2600) which I had set it's default gateway to 192.268.0.1 so I could access both devices. While trying to trouble shoot a VPN issue and change MTU settings on the Synology Router I noticed I began getting the AT&T default gateway from the Nighthawk onto the Synology router (10.*.*.1). I factroy reset both devices but no matter what I do, I'm not getting the IP Passthrough Gateway of 192.168.1.1 of the Nighthawk to the Synology. I keep getting the AT&T Gateway IP address. This is an issue as this address changes everytime there is a reboot of the nighthawk and and it's needed to be able to login to the nighthawk. Any ideas on how to get the 192.168.1.1 address back?