My Archer C5400 v2.0 seems to no longer want to install the static routes I have configured into its routing table. 

This device is at the outer-most edge of my network, and serves as the gateway to my cable model. I have other routers inside the network, connect to the LAN. I can no longer get to devices behind the other routers because the routes for those networks are no longer in C5400's route table, and instead my packets are just following the default route out to the cable provider's network. 

I've tried rebooting (although the problem started after a recent reboot), and I've tried removing and re-installing the static routes, to no avail. 

I confirmed that the firmware I am running is the most recent. 

What can I do, asking from tossing it in the trash and getting a new device (which I'm very close to doing, now)?