Not sure if it's related, but I just noticed my modem which worked perfectly for months has suddenly stopped broadcasting on 5Ghz (just noticed today, but it has probably been going on for a while), and the option to enable it in the firmware has literally disappeared. It's almost like Cox changed the firmware... going to call and find out if they know what's going on.
See my thread I just posted on this issue. Somehow they have literally stripped my ability to use 5Ghz from the firmware. What modem are you using?