Ubuntu 18.04.1 not recognizing Ctrl + Alt

Solution 1:

This is a known issue with GNOME shell, shortcuts get triggered on-keypress instead of on-release (see this). Since you have Ctrl+Alt set to change the keyboard layout, whenever you attempt to press Ctrl+Alt+something, the shell registers only Ctrl+Alt immediately after you've pressed Alt and changes the layout.

You can disable this Ctrl+Alt combination using (GNOME) Tweaks. First install it by running

sudo apt install gnome-tweaks

and use the tool to disable the combination. Refer to this for details: Ubuntu 17.10 and later: can't change the input switching shortcut to alt+shift