Not sure what happened to my other post I just made. It vanished. Did a moderator delete it?
Anyway, if the password was changed, use the Panoramic app to change the SSID and password. See here. There is also a way to do it via 192.168.0.1 but I couldn't find official documentation for that since Cox wants you to do all/most things via the app now.
As for the new device warning, do you have Apple devices? If so, they use "private address" which randomizes the MAC address, which causes your gateway to see it as a new device. See here to disable. You can also use the app to see what devices are connected. See here. If you can get it's MAC address, you can look it up here to see the vendor(manufacture). If no vendor, probably a randomized MAC address.
As for MyCloud, try turning off Advanced Security. See here.