For the last couple of weeks, I've been unable to change the screen brightness. I first noticed it when I switched from mains to battery power - the screen didn't dim like it used to. The slider still appears on screen, and moves when you press Fn and either the left or right arrow keys, but the brightness doesn't change. Using the brightness button on the notifications tab doesn't work either - the % level changes, but again there's no change in actual brightness level.
I'm on Windows 10, all up to date.