Intermittent DOCSIS T4 timeouts causing confirmed internet outages

I've been experiencing sporadic internet disconnections for several months. The outages typically last a few seconds to under a minute.

My equipment:

• Motorola MB8600 DOCSIS 3.1 modem

• UniFi Cloud Gateway Ultra, directly connected to the modem

• CommScope SV-2G two-way splitter, recently replaced by an Xfinity technician

On November 11, 2026, around 12:31 PM Pacific, my UniFi gateway recorded an internet outage that coincided with a critical T4 timeout in the Motorola modem logs at 12:31:43 PM.

The modem subsequently logged upstream channel errors, including "UCD invalid or channel unusable," and diplexer configuration messages.

Additional observations:

• Downstream power ranges from approximately −5 to −10 dBmV.

• The modem is accumulating substantial downstream uncorrectable codeword errors.

• Upstream transmit power is approximately 44–45 dBmV.

• A previous Xfinity technician replaced the splitter and MoCA filter, but the disconnections continued.

• My main house and attached basement ADU have separate Xfinity accounts and modems, sharing an incoming coax feed.

I'm requesting a technical escalation rather than another basic modem-reset troubleshooting session.