Some time ago I replaced the standard Time Warner cable with more expensive cable. I did this despite the fact that my cable reception was fine. But that didn't help. I changed it back to the "authorized" Time Warner cable. So I know it is not the cable. And if it was the cable why would it only happen at night.
Right now my connection is actually working because it is day - now it's working. 2 hours ago was a different story. That is what puzzles me.
Could be water in a splitter, tap, etc. Those signal levels you showed are too low to work a modem. The line appears to not be dedicated. IT probobly isnt the "cable" per se. I imagine the actual cable is good, it's just that you are not on a two way splitter straight from the drop. Can you go out side your home and follow the line from the pole or pedestal to where the cable comes into your home? If so, follow that line and tell me the first passive device it runs into, ground block or splitter. IF it isn't first running into a two way or unbalanced three way splitter (two 7 db legs and one 3.5 db leg), then right there is your problem. Trace that modem line out and put one leg on a two way splitter.
IF it IS, then is the splitter old, damaged? Splitters should be rated for 5-1000 MHz. IF anything less, change it, or have your cable company do it.