We upgraded our primary Management Server from R77.30.03 -> R80.30 with no issues. Few things to check to make sure it goes smoothly.....
- Make sure that you backup you're server before upgraded.
- Check that you have the latest deployment agent
- Use CPUSE to perform the upgrade
- Make sure that you have the latest SmartConsole installed after the upgrade
A few other things that we did was to remove any old client packages that were no longer in use just to free up some space.
Also not sure if this applies with upgrading from R80.20 -> R80.30, but when we went from R77.30.03 -> R80.30 we have to do a clean install of our secondary management server and also all of our policy servers, we could only do an upgrade of our primary management server.