Nightly upstream outage 9:40 PM–3 AM, T3 timeouts + UCD unusable, phone support can't help

Hoping someone here with node access can pick this up, because the phone line has gone nowhere and one call actually dropped me while I was on hold.

I lose internet at basically the same time every night. It goes out around 9:40 PM and doesn't recover until somewhere near 3 AM, then it's rock solid all day. Happened every night for the past 4 days.

Modem is my own Arris SURFboard SB8200. During the outage its event log fills with upstream ranging failures. The two that keep repeating:

Started Unicast Maintenance Ranging - No Response received - T3 time-out
UCD invalid or channel unusable

So it's my modem trying to range against the CMTS on the upstream and getting no response. I've already checked the obvious stuff: upstream transmit power is normal (not pinned high), and downstream SNR is fine. That rules out attenuation on my drop and rules out a downstream problem. What's left is upstream noise or ingress on the node during the evening window.

I know the reflex is to blame the modem, but a box that fails on a fixed schedule and works perfectly the other 18 hours a day isn't broken hardware. The time-lock says environmental, on the shared plant.

Phone reps couldn't see any upstream or CMTS data and had no way to route this to line maintenance, so I'm stuck. What I'm hoping someone here can do:

Pull the upstream signal and noise on my node during the 9:40 - 3:00 window and see if the noise floor is climbing. Check whether other modems on my node are logging errors or flapping in that same window (I'd bet they are). And get a plant/line-maintenance ticket opened rather than an in-home visit, or if a tech does come, schedule it during the failure window and have them meter the return path at the tap and node, because a daytime check will test clean.

Happy to provide the full event log or modem status page if that helps. Just want this in front of someone who can actually see the upstream.