I sent this same post as an email to CoxHelp email. They instructed me to check if the coax was screwed into my modem tightly. How helpful!
HOWEVER, they must have lodged a ticket or this post must have generated some interest because after 3 weeks of jitter, packetloss, and intermittent latency the entire situation cleared up overnight and connection is now rock solid. Like impossibly rock solid.
This is a great turn of events, but also incredibly frustrating. The issue was obviously on their side for weeks (possibly a configuration error?) and affected hundreds of customers using the local node, but my and other neighbors emails and complains were ignored or sent to the lowest level of tech support. Then I bring it to a public forum and the entire issue is instantly corrected. Don't vote with your wallet, vote with your... social media account?