Modem Online, Zero Network Activity

I'm running an XB6 modem/router and I've had just about zero problems for several years, and I appreciate that!

That changed the other night however; on Sunday night while we were asleep, my internet dropped out on both wired and wireless connections. I woke up in the morning and assumed it was likely an outage, but I unplugged the box, gave it 30 seconds or so, then plugged it back in. Once it rebooted, I was pleased to see the internet working again!

A few hours later, my partner and I hop in a Discord call together for her to stream something to me (note: we're in the same house, just separate rooms). We're both connected to the ethernet directly. The stream starts to die. Our voices robot. I do a speed test and find that I'm getting a solid 500-600Mbps download (I'm on the 1GB speeds plan, but the 500-600 is no big deal), but my upload is atrocious; under 2Mbps, often under 1.

So I go into the XFinity app and give it a restart. This time, the modem comes back on but gives me absolutely nothing. No connectivity of any kind.

I've reset the modem to factory settings, checked my coax connection to the wall and the box, ensured it's even been (gently) dusted out in case heat was an issue, but nothing has brought it back to life since then. Any suggestions on additional troubleshooting steps?