[Sephiroth]

This is likely to be a dodgy street box amplifier (evidenced by the varyying power levels).

There could, of course, be a poor connection somewhere that is just about making. So make sure your coax cables are tight at each end. It could also be a dying SH but this is unlikely. It's the first thing a field engineer will change, usually.

Otherwise it's a network team job (not an ordinary field engineer)