I've checked the surrounding area and not showing any issues the would be affecting the modem. Check the modem signal levels and they're not at the levels we like seeing them. You mention you have tried different modem. Have you check the coax cable and make sure there are no kinks and the conductor (copper pin ) is bent or just try swap the coax if you have a spare?
SNR isn't great but it's technically within specs. I don't know if I trust those power levels. All channels perfectly 0 dBmV doesn't seem possible. Maybe someone from Cox can confirm those levels. This doesn't look like an easy answer.
Hello, if still finding concerns over the connection and need us to check anything that could be affecting the connection? We would be happy to do so for you. When available can you please reach us on Twitter at @CoxHelp, visit us on Facebook, or email by at email@example.com for assistance anytime. -Dan