I am running 18.04 with unity and just tested some other Desktops that are installed long time also: LXQt, Budgie, gnome (wayland and xorg). Gnome crashed on both. After relogin to unity the keys didnt work while "sudo showkey" shows that the buttons are working. They even get the function in the Shortcut dialog in the systemsettings.
Turns out it was the "commands" plugin in ccsm that was activated. Installed ccsm, deactivated commands: Buttons work again.
I am running 18.04 with unity and just tested some other Desktops that are installed long time also: LXQt, Budgie, gnome (wayland and xorg). Gnome crashed on both. After relogin to unity the keys didnt work while "sudo showkey" shows that the buttons are working. They even get the function in the Shortcut dialog in the systemsettings.
Turns out it was the "commands" plugin in ccsm that was activated. Installed ccsm, deactivated commands: Buttons work again.