I have the same SMC networks cable modem that I got when I originally signed up for Comcast Business, many years ago. I've noticed that when I list the clients in the web UI, it fetches a JSONP list of mac addresses, names, and IP addresses. Sometimes this list contains the string
Based on the information you have provided I have two potential solutions for you. First is for me to push a factory rest from my end ensuring that the Firmware is up to date and that the modem is re-registered to the network. Next would be to have a tech come out to check the lines and possibly swap the modem. The factory rest usually takes 2-3 minutes but can take up to 40 minutes to complete. Do you have a preferred time of day for this rest?