CM3000 Repeated Cox disconnects with SYNC Timing Synchronization failure

I am providing the results of my further investigation. This assessment comes from a ChatGPT analysis of the CM3000 diagnostic information and event logs:

Observed Technical Symptoms:

1. Modem Diagnostic Status:
   - Startup Procedure: Successfully completes downstream acquisition, DHCP, and provisioning.
   - Cable Diagnostic: Status = Poor | Mode = Partial Service

2. Upstream Bonding (SC-QAM & OFDMA):
   - Channels 1–4 (ATDMA) locked at:
     - Frequencies: 17.6–36.8 MHz
     - Power: 34.0 to 35.0 dBmV
   - Channel 5 and OFDMA Upstream Channel 1 (Channel ID 6 @ 36.8 MHz):
     - Not Locked
     - Power reported = 0 dBmV
     - Modulation/Profile = 11,13
     - Power when it appears = 31.0 dBmV

3. Downstream:
   - All 32 SC-QAM channels locked with SNR from 43.7 to 46.3 dB, power +5.8 to +8.0 dBmV
   - Two OFDM downstream channels locked, minimal correctables, zero uncorrectables

4. DOCSIS Event Log (during each drop):
   - SYNC Timing Synchronization failure – Failed to acquire QAM/QPSK symbol timing
   - RNG-RSP CCAP Commanded Power Exceeds Value
   - Dynamic Range Window violation
   - DHCP Warning – Non-critical field invalid in response
   - Unrecognized OID
   - US profile assignment change

Technical Assessment:

• The modem consistently fails to lock Channel 5 or the OFDMA upstream path (~36.8 MHz), which appears to be required under certain provisioning states or load.
  - OFDMA Channel ID 6 remains in a Not Locked state, often with low reported power (31.0 dBmV), likely below CMTS thresholds or too noisy to maintain sync.
  - The SYNC Timing and RNG-RSP events suggest return path SNR or ingress noise impairments, likely within the 24–40 MHz range, or an upstream profile mismatch with the CMTS.

Advice would be appreciated.

Power is a bit high on some channels. 

What FW is loaded on the modem? 

Please post the Event logs data page so we can see that data. 

Latest firmware is loaded.

Event 

Event Log:

Thanks. The advice from the Cox service rep yesterday was that the modem was at fault. i have requested an elevation of the issue to a higher tier technician. Just curious as to whether my experience is unique or whether others have encountered this issue.

Thanks, iFrog. The first Cox service reps who came out identified a number of issues with the lines, which were probably 30 years old and revealing signal degradation. He replaced every line and connection from the modem out to the street and even some in the local area. The infrastructure is now pristine. Curiously, the upload channel issues appeared only after all the upgrade work was done. 

I did notice that on those occasions when the cable modem connection status shows "Good" the diagnostic information shows that Upstream Channel OFDMA #1 is locked. The modem then (apparently) encounters a condition that flips it "Poor" with OFDMA Channel #1 unlocked.

Thanks iFrog. I posted on the Reddit page.

Also, because I can't edit my last post to add this, I prefer the S33 as it has the 2.5G port and even with a 1G package, having a 2.5 connection gives you the full Gigi so not capped at 940 Mbps.