Solid Green Servie Light - What does it indicate

I have an ATT BGW320-500 (Humax) modem/router. Firmware 6.28.7.
It's working fine.
My wired ethernet devices (PCs, Roku etc) are connected to this router.
All my WiFi devices are connected to my TP-Link Deco mesh network where the main node has a wired connection to the ATT device.
I recently disabled WiFi on the ATT device. Everything continues to work as expected. No restarts required.

The only thing that changed is the service light on the front of the ATT modem changed from solid white to solid green and stayed that way. I've never seen this before, and am unable to find an explanation for a solid green light.

Any suggestions?