I was wondering why this shortcut to add new constraints did not work for me and stumbled on this post (https://community.amd.com/t5/pc-drivers-software/amd-relive-interfering-with-ctrl-shift-letter-shortcuts-in-other/td-p/276452) Turns out AMD software uses it and it is disabled in any application including blender. To enable the shortcut disable it here: 
Hope someone will find this useful.
