Testing Xubuntu 18.04: Keyboard key for adjusting screen brightness not working anymore

[Willem Hobers]

Devs,

Today I noticed that, with Xubuntu 18.04, the keyboard key to adjust 
screen brightness is not working anymore. The keys to adjust volume (up, 
down, mute) still work.

I'm confident that, in 18.04, the brightness key worked before, as I use 
that key on a daily basis.

The last time I updated the daily was yesterday.

Any advice on how to investigate this issue?

Is there more information I can provide?

Kind regards,

Willem

I ran lshw, and copied information about the laptop I'm using:

     description: Notebook
     product: 80UD (LENOVO_MT_80UD_BU_idea_FM_Lenovo ideapad 110-15ISK)
     vendor: LENOVO
     version: Lenovo ideapad 110-15ISK