Does the problem happen if you connect a PC direct to the S33? Remember to power cycle each time you change what the ethernet from the modem is plugged into.
Also, I didn't mean if there was anything in that room, but if you had splitters/amps/filters somewhere in the house or outside the house. Like how many outlets do you have in your house? If more then 1, there should be a splitter connecting the two.
Next, post your signal levels from 192.168.100.1 as seen here. You can also post the event logs from around the time of the issue but be sure to edit out the HFC MAC address.
Last, what modem router do you have?