Consistent DOCSIS internet interruptions occurring daily

Customer Equipment

• NETGEAR Nighthawk CAX30 cable modem/router
• Firmware: v2.2.4.2
• Xfinity 1 Gbps Internet plan
• Modem/router normally located upstairs
• Several devices are hardwired by Ethernet; Wi-Fi coverage is strong throughout the home

Primary Problem

Internet service has been experiencing recurring brief outages for approximately the last two months, with the problem becoming noticeable as a consistent pattern.

The service frequently drops in the evening, generally around 6:40–6:45 PM, although the broader recurring problem has been occurring during the evening hours.

The outage typically lasts approximately 2–5 minutes, after which the CAX30 reacquires service without the customer manually rebooting it.

This is an ongoing problem rather than an isolated or occasional outage.

Symptoms During Outage

The CAX30 remains powered and Wi-Fi remains available locally, but Internet connectivity is lost.

During the most recent outage, the modem event log captured the following sequence:

• SYNC Timing Synchronization Failure – Failed to acquire QAM/QPSK symbol timing
• MDD Message Timeout
• T4 Timeout – Response to Broadcast Maintenance Request received, but no Unicast Maintenance opportunities received
• UCD Invalid or Channel Unusable
• Repeated T3 Timeouts – No Ranging Response received
• Downstream profile reassignment during recovery
• Modem then reacquires downstream/upstream channels and Internet access returns

Relevant CMTS MAC shown in modem log:

[Edited: "Personal Information - MAC Address"]

Most Recent Documented Failure

Approximate customer-observed outage time:

August 12, 2026 – approximately 5:42 PM

Modem log entries associated with the event begin around:

17:40:49–17:43:13 according to the modem event-log clock

The failure sequence included multiple SYNC failures, T4 timeouts, MDD timeout, UCD/channel-unusable events, and T3 ranging timeouts.

The service recovered automatically several minutes later.

Interior Coax Troubleshooting Completed

Outside Distribution

The original outside configuration included an Amphenol multi-port coax distribution splitter.

Because only one coax outlet is currently needed for the CAX30, the active modem line was identified with a continuity test and the multi-port distribution splitter was bypassed.

Cable Run Identification

The active upstairs CAX30 coax run was positively identified using a continuity test.

The entire run was physically traced through the attic/crawlspace.

Findings:

• Approximate total run length: 60–75 feet
• One continuous coax run from the outside service area to the upstairs room
• No hidden splitter found
• No hidden barrel connector/junction found
• Cable remains accessible in attic and was visually inspected

Upstairs Wall Plate

The F81 wall-plate barrel connector was replaced with a new 3 GHz 75-ohm F81 connector.

Modem Jumper

The coax jumper from the wall plate to the CAX30 was replaced with a new RG6 coax cable.

All coax connections were checked and tightened.

Direct Service-Feed Test

The CAX30 was temporarily connected directly at the outside service feed to establish a baseline.

Approximate readings:

• Downstream power: +6 to +8 dBmV
• Downstream SNR: approximately 39–40 dB
• Upstream transmit power: approximately 38 dBmV
• No significant uncorrectable-codeword issue noted immediately after connection

This demonstrated that the CAX30 itself operates normally when connected directly to the incoming service.

Upstairs In-Wall Run Test

The CAX30 was then connected upstairs directly to the in-wall coax, temporarily bypassing the wall plate and short jumper.

Approximate readings:

• Downstream power: approximately −2 to −4.4 dBmV
• Downstream SNR: approximately 38.5–39.9 dB
• Upstream power: approximately 45–46 dBmV
• OFDM downstream levels approximately −3 to −7 dBmV
• Zero uncorrectables immediately after test connection
• All downstream and upstream channels locked

Internet performance during this configuration was strong.

Final Restored Configuration

After replacing the wall-plate F81 and modem jumper, the CAX30 was returned to its normal upstairs position.

Current healthy readings before/after the recurring outage:

Downstream

• Approximately −2.1 to −3.6 dBmV
• SNR approximately 39–40 dB
• 32 downstream QAM channels locked

Upstream

• Four ATDMA upstream channels locked
• Approximately 45.8–46.0 dBmV

OFDM

• Channel 193: approximately −4.1 dBmV / 39.2 dB MER
• Channel 194: approximately −8.3 dBmV / 37.6 dB MER
• OFDM uncorrectable codewords: 0 at the time captured

NETGEAR Cable Diagnostic reports:

Status: Good

Internet Access, Downstream Status, and Upstream Status all return green immediately after recovery.

Speed Testing

From an iPhone located next to the CAX30:

2.4 GHz Wi-Fi

• Approximately 105 Mbps download
• Approximately 37.4 Mbps upload

5 GHz Wi-Fi

• Approximately 764 Mbps download
• Approximately 40.8 Mbps upload

The 764 Mbps result was the fastest Wi-Fi speed recorded on that device.

This supports that the router, local network, and normal upstream/downstream capacity are functioning well outside the brief outage window.

Community Corroboration

On August 12, 2026, a discussion in a local community group produced multiple independent reports from nearby Xfinity customers describing similar recurring service interruptions.

Reported symptoms included:

• Internet/TV service going down regularly or daily
• Multiple reports that the outages occur primarily in the evening
• Outages commonly lasting approximately 2–10 minutes before service returns
• Reports from customers in the Cashtown, McKnightstown, Seven Stars and surrounding area
• Several residents reporting that problems began or became more noticeable following Xfinity network work/upgrades in the area approximately two months ago
• One nearby resident specifically reported recurring evening outages lasting approximately 2–5 minutes, closely matching the problem documented at this residence
• Other residents reported continuing intermittent outages despite previous Xfinity service visits

Not every nearby customer reports being affected, which may indicate that the problem is limited to a particular node, service group, amplifier leg, return path, or other portion of the local cable plantrather than affecting the entire Xfinity system.

These community reports are not being presented as proof of a specific technical cause, but they provide significant corroboration that the recurring problem is not isolated to this residence.

Diagnostic Conclusion

The recurring outage has continued for approximately the last two months and persisted after extensive troubleshooting of the customer-side coax path, including:

• Bypassing the outside multi-port distribution splitter
• Positively identifying the active modem coax
• Inspecting and tracing the entire in-home coax run
• Confirming no hidden attic splitter or barrel junction
• Replacing the upstairs wall-plate F81
• Replacing the modem coax jumper
• Tightening all accessible connections
• Verifying healthy modem RF levels immediately before and after the event
• Verifying strong real-world Internet throughput

The modem repeatedly logs a DOCSIS loss-of-communication sequence involving:

SYNC failures → MDD timeout → T4 timeout → UCD/channel unusable → T3 ranging failures → reacquisition

Healthy RF levels return immediately following the outage.

Multiple nearby Xfinity customers are also independently reporting similar recurring short-duration outages, particularly during evening hours.

Taken together, the modem diagnostics, controlled in-home testing, recurring timing, and nearby customer reports strongly justify investigation of the Xfinity drop / tap / upstream return path / amplifier / node / service group / CMTS side rather than continued troubleshooting of the customer’s internal network.

Requested Technician Action

Please investigate for an intermittent outside-plant or return-path issue, including:

• Drop from residence to tap
• Tap condition
• Connectors/fittings outside the residence
• Upstream return-path noise or ingress
• Intermittent upstream impairment
• Amplifier/active plant performance
• Node/segment/service-group health
• CMTS communication history for this modem
• Whether other modems on the same node or service group show T3/T4/SYNC/MDD events during the same evening periods
• Whether Xfinity has open maintenance issues or recent upgrade work associated with this service area
• Plant conditions or scheduled activity occurring during the recurring evening outage period, particularly around 6:40–6:45 PM

Please correlate the modem’s T3/T4/SYNC/MDD events with Xfinity plant telemetry and other modems on the same service group rather than limiting troubleshooting to an interior wiring inspection, modem reboot, or modem replacement.