Comment 15 for bug 1188569

For Unity (18.10, 18.04):

1) All default shortcuts (super+L, ctrl+alt+l) works on fresh install. For some people toggling custom-commands from ccsm (compiz-config-settings-manager) makes everything works. But hard to reproduce.

2) Custom keybinding shortcuts will not work until a re-login. Possibly a bug in unity-settings-daemon. see bug #1435020

3) Print-screen, alt+Print-screen have some problem with key-press vs key-release due to ubuntu removing 6 years old xorg patch. see LP: #1683383

4) Key combination which are hard-coded (ex. ctrl+alt+backspace to kill x-server) doesn't not if it is set to do other things. Possibly bug in u-s-d.

5) Media keys (Volume and Mute etc) doesn't work for some people. But it is most likely device specific. For me it works. Some make it work after restarting u-s-d (unity-settings-daemon -r &) or toggling commands plugin from ccsm. See bug #1727842

To debug properly do this on fresh install:

1) Open terminal on unity.
2) Run "unity-settings-daemon -r --debug", keep it open
3) Now Try removing existing custom shortcut from Unity control center -> keyboard -> shortcuts
4) Try re-adding the shortcut.
5) Paste the output from terminal on

Other sessions with g-s-d:
For gnome sessions it could be this bug #1750846, though I am not sure.