I appreciate your help with my problem. I called and requested that a cable tech comes on site to take a look. They verified that all lines were good and that signal levels were where they needed to be. After insisting that there was an issue/some kind of failing component they further investigated the lines to find a splitter in the basement with filters on them for whole home DVR. We no longer use cable for TV. The tech explained that without the set-top boxes to balance out the signal, it could be causing interference over the lines.
I still don't understand why the issue took several months after deactivating the TV service to present itself, or why it only seemed to cause problems during the night, but we are coming up on 48 hours without any reboots.
Thanks again for all the help!