Intermittent upstream impairment - T3/T4 timeouts, CMTS not answering, modem re-registration (3, 5 and 6 Nov)

Customer-owned NETGEAR CM2000 (firmware V8.01.02), 1000/40 plan. My router
monitors the connection continuously. All times are MST.

On three days this month the connection was impaired in ways that point at the
upstream (return path). On 6 Nov the modem log shows ranging failures on two
upstream channels, ending in a re-registration. Current levels look fine, so a
remote check right now will look clean.

6 Nov (worst day)
- Packet loss at normal latency (13-18 ms), IPv4 and IPv6 together, in bursts
  at 09:38-09:45, 13:38, 14:15-14:33 and 16:37-16:44.
- Modem log, last burst:
    16:38:25  16 consecutive T3 timeouts on upstream channels 1 and 3,
              "Unicast Maintenance Ranging attempted - No response - Retries exhausted"
    16:38:54-16:40:55  CM-STATUS event 7 (T3 retries exceeded) on upstream
              channel IDs 49 and 51, every 30 s
    16:42:33 and 16:42:37  T4 time-outs
    16:42:50-16:43:07  re-registration (MDD, config file)
- Router side, same burst: a DHCPv6 client on my router was sending a Solicit
  to the CMTS about every 2 minutes (a bug on my side, since fixed, that
  happened to make a good probe). The CMTS normally answered within a second.
  The Solicits at 16:37:42, 16:39:52 and 16:42:00 got no answer. The first
  answer came at 16:43:57, right after the re-registration. Between 09:00 and
  18:00, 22 of 271 Solicits went unanswered. The modem's Ethernet link stayed
  up throughout.
- The loss stopped at 16:44, right after the re-registration.

5 Nov
- 11:12-15:02: the CMTS failed to answer 17 Solicits (about 4 an hour, against
  0.6 an hour the rest of the day). In that window an IPv4 health-check ping
  timed out at 12:54 and my router's failover tripped at 14:04.

3 Nov
- 09:51-12:40, in three parts: latency up to 5.4 s, then loss up to 97%.
  Xfinity texted me at 10:58 about an area "network performance issue", and at
  13:51 that the work was completed. Before that, my last area-outage text was
  in early July. 6 Nov came three days after the "completed work".

7 Nov (modem log, minor; my router saw no impact)
- 11:13 RNG-RSP "CCAP Commanded Power in Excess of 6 dB Below the Value
  Corresponding to the Top of the DRW"
- 15:32 one T3 timeout
- 17:43 OFDM PLC/NCP failure and recovery on DS channel 48

Current levels (8 Nov 07:42): DS 31 of 32 SC-QAM locked at +7.5 to +8.4 dBmV,
SNR 40.6-41.8 dB; OFDM MER 38.9 dB; US 4 ATDMA channels at 37.8-39.0 dBmV.
Uncorrectables are low: 1,240 on the primary, 53 on one other channel, 7,519 on
OFDM. The modem's event log holds only about 40 entries, so nothing before
6 Nov 16:38 survives.

Could someone please:
1. Check upstream SNR/MER and pre-equalization history for upstream channel
   IDs 49 and 51 on 5 and 6 Nov?
2. Check whether other modems on my node logged T3 timeouts at 16:38 on 6 Nov?
   That would show whether it's the node or my drop.
3. Send a line tech if the node, tap or drop needs work?

Happy to DM account details. The full modem diagnostic, with MAC addresses
removed, is below.

Cable Diagnostic

Status: Good

Action:
Your setup looks fine. If you can't access the internet, make sure you properly activated the modem. If modem has been activated and you still can't access the internet, contact your service provider for troubleshooting help.
If you can access the internet but has other internet issue, the Netgear Cable Knowledge Base can provide additional troubleshooting info.

CM Status: Good

Downstream Status: Good

    Downstream Power Level: Good

    Downstream SNR Level: Good

Upstream Status: Good

    Upstream Power Level: Good

Current Time: Sun Nov 08 07:42:26 2026

Startup Procedure
Acquire Downstream Channel: 531000000 Hz  Locked
Connectivity State:          OK       Operational
Boot State:                  OK       Operational
Security:                   Enabled   BPI+
IP Provisioning Mode:       Honor MDD   IPv6 only

Downstream Bonded Channels
Channel LockedStatus Modulation ChannelID  Frequency     Power    SNR   Correctables Uncorrectables     
      1     Locked     QAM256     28     531000000 Hz     7.9     41     887     1240
      2     Locked     QAM256      4     381000000 Hz     8.2     41.7     6     0
      3     Locked     QAM256      5     387000000 Hz     8.2     41.7     2     0
      4     Locked     QAM256      6     393000000 Hz     8.4     41.8     2     0
      5     Locked     QAM256      7     399000000 Hz     8.3     41.7     1     0
      6     Locked     QAM256      8     405000000 Hz     8.2     41.5     2     0
      7     Locked     QAM256      9     411000000 Hz     8.1     41.4     7     0
      8     Locked     QAM256     10     417000000 Hz     8.2     41.4     1     0
      9     Locked     QAM256     11     423000000 Hz     8.2     41.4     8     0
     10     Locked     QAM256     12     429000000 Hz     8.3     41.4     6     0
     11     Locked     QAM256     13     435000000 Hz     8.3     41.5     6     0
     12     Locked     QAM256     14     447000000 Hz     8.3     41.4     2     0
     13     Locked     QAM256     15     453000000 Hz     8.2     41.4     1     0
     14     Locked     QAM256     16     459000000 Hz     8.2     41.2     1     0
     15     Locked     QAM256     17     465000000 Hz     8.1     41.2     6     0
     16     Locked     QAM256     18     471000000 Hz     8.2     41.1     2     0
     17     Locked     QAM256     19     477000000 Hz     8.2     41.2     18     53
     18     Locked     QAM256     20     483000000 Hz     8.2     41.2     2     0
     19     Locked     QAM256     21     489000000 Hz     8.2     41.3     2     0
     20     Locked     QAM256     22     495000000 Hz     8.3     41.3     4     0
     21     Locked     QAM256     23     501000000 Hz     8.1     41.3     2     0
     22     Locked     QAM256     24     507000000 Hz     8     41.3     7     0
     23     Locked     QAM256     25     513000000 Hz     8     41.3     4     0
     24     Locked     QAM256     26     519000000 Hz     8     41.2     4     0
     25     Locked     QAM256     27     525000000 Hz     7.9     41     4     0
     26     Locked     QAM256     29     543000000 Hz     7.7     40.8     5     0
     27     Locked     QAM256     30     555000000 Hz     7.5     40.8     4     0
     28     Locked     QAM256     31     561000000 Hz     7.5     40.8     5     0
     29     Locked     QAM256     32     567000000 Hz     7.6     40.7     6     0
     30     Locked     QAM256     33     573000000 Hz     7.6     40.6     7     0
     31     Locked     QAM256     34     579000000 Hz     7.5     40.6     5     0
     32     Not Locked     Unknown      0     0 Hz     0.0     0.0     0     0

Upstream Bonded Channels
Channel   LockedStatus  ChannelType ChannelID   SymbolRate        Frequency       Power     
      1       Locked       ATDMA     50       5120 Ksym/sec       22800000 Hz       38.5 dBmV
      2       Locked       ATDMA     49       5120 Ksym/sec       16400000 Hz       37.8 dBmV
      3       Locked       ATDMA     51       5120 Ksym/sec       29200000 Hz       39.0 dBmV
      4       Locked       ATDMA     52       5120 Ksym/sec       35600000 Hz       39.0 dBmV
      5       Not Locked       Unknown      0       0       0       0.0
      6       Not Locked       Unknown      0       0       0       0.0
      7       Not Locked       Unknown      0       0       0       0.0
      8       Not Locked       Unknown      0       0       0       0.0

Downstream OFDM Channels
Channel   LockedStatus  ProfileID  ChannelID    Frequency       Power       SNR/MER    ActiveSubcarrier    Unerror    Correctable   Uncorrectable
      1     Locked     0 ,1 ,2 ,3     48     722000000 Hz     7.38 dBmV     38.9 dB     928 ~ 3167     73343102076     72710865465     7519
      2     Not Locked     0      0     0 Hz     0 dBmV     0 dB     0 ~ 4095     0     0     0

Upstream OFDMA Channels
Channel   LockedStatus    ProfileID    ChannelID    Frequency       Power
      1     Not Locked     0      0     0 Hz     0 dBmV
      2     Not Locked     0      0     0 Hz     0 dBmV

Event Log
         Time               Priority     Description
Sat Nov 07 17:44:07 2026     Notice (6)     CM-STATUS message sent. Event Type Code: 24; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0 1 2 3.
Sat Nov 07 17:43:43 2026     Notice (6)     CM-STATUS message sent. Event Type Code: 24; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 0 1 2.
Sat Nov 07 17:43:39 2026     Notice (6)     CM-STATUS message sent. Event Type Code: 16; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: 3.
Sat Nov 07 17:43:37 2026     Notice (6)     CM-STATUS message sent. Event Type Code: 22; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.
Sat Nov 07 17:43:37 2026     Notice (6)     CM-STATUS message sent. Event Type Code: 23; Chan ID: 48; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.
Sat Nov 07 15:32:34 2026     Critical (3)     Started Unicast Maintenance Ranging - No Response received - T3 time-out
Sat Nov 07 11:13:29 2026     Warning (5)     RNG-RSP CCAP Commanded Power in Excess of 6 dB Below the Value Corresponding to the Top of the DRW
Fri Nov 06 16:43:07 2026     Notice (6)     DS profile assignment change. DS Chan ID: 32; Previous Profile: ; New Profile: 1 2 3.
Fri Nov 06 16:43:06 2026     Notice (6)     TLV-11 - unrecognized OID
Fri Nov 06 16:42:50 2026     Notice (6)     Honoring MDD; IP provisioning mode = IPv6
Fri Nov 06 16:42:46 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:42:37 2026     Warning (5)     ToD request sent - No Response received
Fri Nov 06 16:42:37 2026     Critical (3)     Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out
Fri Nov 06 16:42:35 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:42:33 2026     Critical (3)     Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out
Fri Nov 06 16:42:20 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:40:55 2026     Notice (6)     CM-STATUS message sent. Event Type Code: 7; Chan ID: 49 51; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.
Fri Nov 06 16:40:42 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:40:24 2026     Notice (6)     CM-STATUS message sent. Event Type Code: 7; Chan ID: 49 51; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.
Fri Nov 06 16:40:18 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:39:54 2026     Notice (6)     CM-STATUS message sent. Event Type Code: 7; Chan ID: 49 51; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.
Fri Nov 06 16:39:36 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:39:24 2026     Notice (6)     CM-STATUS message sent. Event Type Code: 7; Chan ID: 49 51; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.
Fri Nov 06 16:39:01 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:38:54 2026     Notice (6)     CM-STATUS message sent. Event Type Code: 7; Chan ID: 49 51; DSID: N/A; MAC Addr: N/A; OFDM/OFDMA Profile ID: N/A.
Fri Nov 06 16:38:41 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:38:36 2026     Critical (3)     Started Unicast Maintenance Ranging - No Response received - T3 time-out
Fri Nov 06 16:38:33 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:38:33 2026     Critical (3)     Started Unicast Maintenance Ranging - No Response received - T3 time-out
Fri Nov 06 16:38:29 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:38:29 2026     Critical (3)     Started Unicast Maintenance Ranging - No Response received - T3 time-out
Fri Nov 06 16:38:29 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:38:28 2026     Critical (3)     Started Unicast Maintenance Ranging - No Response received - T3 time-out
Fri Nov 06 16:38:28 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:38:27 2026     Critical (3)     Started Unicast Maintenance Ranging - No Response received - T3 time-out
Fri Nov 06 16:38:27 2026     Critical (3)     No Ranging Response received - T3 time-out
Fri Nov 06 16:38:25 2026     Critical (3)     16 consecutive T3 timeouts while trying to range on upstream channel 3
Fri Nov 06 16:38:25 2026     Critical (3)     Unicast Maintenance Ranging attempted - No response - Retries exhausted
Fri Nov 06 16:38:25 2026     Critical (3)     Started Unicast Maintenance Ranging - No Response received - T3 time-out
Fri Nov 06 16:38:25 2026     Critical (3)     16 consecutive T3 timeouts while trying to range on upstream channel 1