I can't add artboards by clicking the + . Plus icon don't appear alongside artboards in the document.
Before the upgrade, everything worked. Today I updated the CC and the icon was gone.
OK if you are sure that you have the artboard tool and it is not working I would do the following - in this order.
1. Try resetting the artboard tool
2. Check Preferences Performance GPU is on - artboards are optimised for the Advanced drawing mode
3. Try resetting preferences (you will need to quit and restart Photoshop)