I have no information about congestion on Cable networks, so I would have to defer to the technicians diagnosis on this. Noise on the network can affect performance and I would expect the technician to have raised an issue so that the network can be investigated further.
Noise within the HFC network could affect a number of services.
Have you returned to using the new Cable modem as it appears that using the old one will not make any change?
- Shelly