Try a factory reset and setup from scratch on the modem.
Netgear has set up a community forum specifically for the Cable Modem products. Most of the people who watch that forum are more likely to have experience with Cable modems and know how to work it better than those of us who follow this router forum. Might be more likely to find someone who has a solution if the question is posted there: https://community.netgear.com/t5/Cable-Modems-Routers/bd-p/home-cable-modems-routers
