Need help with Arris Surfboard SBG8300

I’ve been using my Arris Surfboard SBG8300 modem and router for 4-5 years with no issue. Over night (working at 2am, not working at 7am), the modem-router stopped allowing a connection to the internet.

Both LEDs on the front panel are solid green, though the WiFi light will occasionally flicker a bit without fully flashing. I have no problems accessing the admin panel. When I go into the admin panel, it notes that WAN internet is inactive.

I’ve tried restarting, power cycling and a full factory reset. I’ve also tried manipulating the coax cable. I unfortunately don’t have anything that can test using an Ethernet instead of WiFi.

ISP is Optimum and we have a 500mb plan.

ISP said it is likely an issue with the modem-router and it will likely need to be replaced, but is sending out a tech tomorrow. Any other troubleshooting I can do/any thoughts on what might be the issue?