I upgraded Ubuntu to 17.10 and found out that alt key has strange behavior.
If I press Alt+Space, for example, I can see the menu of the active window, but If I press more complicated combination like Ctrl+Shift+Alt+some_letter, it doesn't react. In Ubuntu 17.04 it worked.
The only way of solving this problem I know is to use gnome-tweak-tool. In this gnome-tweak-tool, I can swap key Win (Super) with key Alt. In this case everything works great, but... I would like key Win to be key Win and key Alt to be key Alt. So, may be there is a good solution for this problem?