Started Unicast Maintenance Ranging - No Response received - T3 time-out

This indicates a problem on your upstream connection. Confirm that all connections are tight. Replace interior cables with brand new high quality RG6 if practical. Remove all unnecessary splitters. If problems persist, contact Cox and request a tech visit as T3 timeouts are often caused by problems outside the boundaries of your property. Post your modem signals and full logs for more complete advice.