CM3000 – repeated T3 timeouts, SYNC failures, intermittent disconnects

Hi Abby, thanks for the reply.

Timing: It's not limited to one part of the day — I get it throughout. The download latency is fairly consistent whenever I'm active (elevated ping with spikes to 500ms+), and the disconnects can happen anytime, including while gaming in the evening. The T3 timeouts in the modem log do cluster somewhat in the afternoon/evening peak window, but they also occur at other times, including overnight. So there are really two things happening: constant latency/instability, plus clustered T3/SYNC events on top of it.

Troubleshooting already completed (this has been exhaustive on my end):

• Power-cycled the modem many times — both via the Xfinity app and physical unplugs
• Restarted and reconfigured the router multiple times
• Verified the coax path myself: single ~10 ft drop from the side of the house to the modem, no splitters, connectors hand-tight
• Had a technician on-site — he metered signal at the tap/street and at the house and confirmed the outside plant and drop are clean; the problem has persisted since his visit
• Captured the full modem signal tables (downstream + upstream) and event logs. Note: the modem only retains about 5 weeks of event history, but this problem long predates that — I've been dealing with it far longer; 5 weeks is simply as far back as the log buffer goes
• Confirmed downstream is pristine (31 channels locked, SNR 40–42 dB, power in spec, zero uncorrectables), which isolates the problem to the upstream/return path
• Identified my firmware as V6.01.04 (the successor to the pulled V6.01.03) and am aware of its reported upstream issues
• Per the tech's suggestion, I'm eliminating any possible premises interference (dedicated clean power, separating and relocating equipment/cabling) — but the T3 timeouts and SYNC failures are DOCSIS-layer upstream events that occur independent of my LAN setup

Key evidence: In just the ~5 weeks the modem's log even retains, there are 27+ Critical T3 timeouts and the frequency is increasing — including "16 consecutive T3 timeouts while trying to range on upstream channel 1 – retries exhausted," plus repeated SYNC timing failures. This has been ongoing much longer; the log only captures the most recent window. Upstream transmit power is also elevated at ~43 dBmV on a ~10 ft drop with no splitters.

Given that reboots, a tech visit, and premises remediation haven't resolved it, could you check my upstream/return-path signal and SNR at the CMTS, look for ingress/noise on my node, and verify my firmware? I'd like this escalated to maintenance / advanced repair rather than another basic tech visit. Happy to share account details by private message.