I've been working directly with the Netgear engineering team on this, and have a couple of updates for those who are following:
1) I changed from a 6DB to a 10DB attenuator and that reduced the number of disconnects, but did not eliminate them.
2) This morning Netgear sent me a beta firmware release (v184.108.40.206). In their words, "Cox’s CMTS frequently performs load balancing which is not common and it may affect CAX80. I have a new firmware that have a newer codebase that may help."
As soon as I installed the new firmware, my upstream power levels went up 3-6 points beyond the boost they got from the attenuator. And I haven't had an error or a disconnect in 48 hours.