Recurring evening latency spikes to 900ms with packet loss - signals clean, T3 timeouts back Aug 20 after May repair

Wired PC, customer-owned Motorola DOCSIS 3.1 modem, no in-home splitter (a technician removed the extra one earlier this year).

SYMPTOM
Bursts of 45-50 seconds where latency goes from about 25ms to 900ms with roughly 1% packet loss, several times an hour, mostly in the evening. Speeds stay at provisioned rates the whole time (972 down / 42 up), so a speed test does not show it.

WHAT I HAVE ALREADY RULED OUT (measured)
22-minute ping trace, 659 probes per target, from a wired PC on an idle connection:

• My own router: median 0ms, max 4ms, zero loss, for the entire window
• 1.1.1.1: median 27ms, peak 882ms, 0.9% loss
• 8.8.8.8: median 25ms, peak 955ms, 1.2% loss

Both public targets degraded in the SAME SECOND on 24 occasions, so this is not one destination or one peer. The connection was idle, so it is not congestion on my side or buffer bloat in my own router.

MODEM SIGNAL (all in spec)

• Downstream: +7.3 to +9.7 dBmV, SNR 40-42 dB, zero uncorrectables on all 32 QAM channels
• OFDM ch 193: 860 uncorrectables - the only channel with any errors
• Upstream: +38 to +42 dBmV across 6 SC-QAM channels

MODEM EVENT LOG - T3 upstream ranging timeouts by month (boot-time retries excluded)
April 15, May 8, June 0, July 0, August 2.
Also a full loss of sync with T4 timeouts on Apr 30, and an OFDM profile change on ch 193 on Aug 20.

Please note the shape of that. It was bad in the spring, a technician visit resolved it, it was completely clean for June and July, and it came back on Aug 20 and again on Aug 25. This is a recurrence after a completed repair, not a new complaint.

WHAT I AM ASKING FOR

• CMTS-side flap list and upstream SNR for my modem
• A check on node utilization during evening hours, roughly 9-10pm local
• If neighbors on the node are affected, a maintenance ticket rather than a premises dispatch

I have the full trace, per-episode timings and the raw event log and can provide them on request. One note to save a step: a reboot and a speed test will both come back normal, and 32 of 33 downstream channels report zero uncorrectable errors, so a modem swap is unlikely to help here.