This reminds of the first cable modem I installed for my brother. It was a DIY kit from his cable provider Suddenlink.
I just could not make it work. So, we called for their service tech.
There was definitely a signal strength problem. He replaced splitter and coax connectors at the house. That improved the TV (analog) signal noticeably, but the modem was still unhappy. He then went looking for the feeder line out in the street and replaced the connections there and that did the trick. Corrosion and weathering takes its toll over the years.
I just could not make it work. So, we called for their service tech.
There was definitely a signal strength problem. He replaced splitter and coax connectors at the house. That improved the TV (analog) signal noticeably, but the modem was still unhappy. He then went looking for the feeder line out in the street and replaced the connections there and that did the trick. Corrosion and weathering takes its toll over the years.