Diagnosis
A solid orange light means the router has power but has lost its connection to the internet from your modem. It's not a device error; it's a 'no signal' status.
How to Fix It
This is almost always a modem or cable issue. 1) Check the Ethernet cable connecting the Nest Wifi Pro's WAN port (the globe icon) to your modem. Unplug it from both ends and plug it back in firmly. 2) Unplug your modem from power for 60 seconds, then plug it back in and wait for all its lights to settle. 3) Finally, unplug your Nest Wifi Pro for 30 seconds and plug it back in. It should go through a boot sequence (white light) and then settle on a solid white light when the internet is back.
If That Didn't Work
Try a different Ethernet cable if you have one. The cable itself might have gone bad, which happens more often than you'd think.
Heads Up
If your modem requires special settings (like PPPoE credentials from your ISP), you needed to enter those in the Google Home app during initial setup. If you just switched modems, you might need to go back into the app's WiFi settings to re-enter that info.