Since upgrading to macOS Sierra (10.12.1 non-beta), I can no longer enter the keyboard combination Command+Shift+Up Arrow or Command+Shift+Down Arrow. I use this in text editors to select everything above or below my text cursor. On the macOS Keyboard Viewer, when I press the combination, only the Command and Shift keys show as pressed down.
Command+Shift+Left/Right Arrow works just fine though.
I'm not sure what's going on. I haven't found anyone else with this problem on Sierra. I used to have Karabiner installed, but uninstalled it after finding it wasn't compatible with Sierra. I also had Karabiner Elements installed for a bit, but uninstalled it as well. Restarting doesn't do anything to change the problem. The problem occurs on both my MacBook Pro keyboard and my external keyboard.