CM1100 won't connect to routers

Yes, it has been working since February 2024. This morning, the Firewalla began reporting the main network interface (connected to the CM1100) was down and that it had switched to the failover cellular backup. The cellular failover has the option to direct connect with Ethernet, so I connected the cellular to the router WAN port, confirmed the link to the router and had internet access on the router.

In troubleshooting, I can see the router WAN port is connected at 2.5Gb, but that there is no activity between the router WAN port and CM1100 LAN 1.

The ISP confirms that the signal is within spec and the CM1100 successfully bonds the upstream/downstream channels and connects to the network from their side.

The ISP also "reset" the modem (their words) and assigned a new IP address. This made no difference in the connection to the router.

That's when I direct connected, to rule out the CM1100 as the issue; however the CM1100 will connect directly (on both LAN ports) but will not connect to the original or backup router I tried. It seems odd that it wouldn't work with ANY router - they can't all be bad, especially since both can connect to the cellular modem.

I also tried a new modem from the ISP - it connects to both routers as well.

I also just finished connecting my network switch directly to the modem after disconnecting all but the laptop I'd used to troubleshoot, and it works.

So the only thing that doesn't work is CM100 -> Any Router.