Dear @rolandua!
It is known problem (see my post as example). I have prepared the fix for 16.04 LTS (with HWE) and 18.04 LTS.
The fix - you should add my PPA (This PPA contains Xorg packages with patch from from ArchLinux AUR ) to the system and install packages from it with the commands below:
sudo add-apt-repository ppa:nrbrtx/xorg-hotkeys
sudo apt-get update
sudo apt-get dist-upgrade
Hope this helps!