Also affects me on Lubuntu 16.04.
Installing IBus (sudo apt ibus) and using Preferences > Language Support to change the Keyboard input method system to IBus, followed by a system reboot, has fixed the issue (compose:ralt in Keyboard Layout Handler now functions as expected).
Also affects me on Lubuntu 16.04.
Installing IBus (sudo apt ibus) and using Preferences > Language Support to change the Keyboard input method system to IBus, followed by a system reboot, has fixed the issue (compose:ralt in Keyboard Layout Handler now functions as expected).