Tool/software: Code Composer Studio
Debian Sid (Linux 4.12.0-1) - Firefox 52.3.0 - CCSv7.3.0
I had this "Warning! Not connected to the cloud server" issue and no matter how I changed my proxy settings in CCS it never got better. I even uninstalled CCS and hunted through my folders for anything named TI and deleted it. Then I had an idea to start CCS in a terminal to see what debug says. Sure enough in the debug messages it talked about trying to go through a proxy I sometimes use. I looked through all my web settings until I got to Firefox (which is my second browser so figuring out it was involved or even installed was a lot of head scratching) and sure enough there the proxy info was. After disabling it and restarting CCS cloud server access was instantly restored.
If you're on Linux it might be worth taking a look at.