I am running Ubuntu 17.04 on a Dell XPS 15 (9560) and it's been working well for over a month. A few days ago I suddenly started having issues with the Fn-shortcuts for brightness and volume.
Brightness keys do not work at all however I can still adjust brightness with the slider in the Brightness & Lock settings
Volume up, down and mute work, but it takes about 30 seconds from when the button is pressed to when the volume is actually changed. I also don't get any OSD notification about the volume change.
xev I could see that the media keys trigger
XF86AudioRaiseVolume etc immediately on keypress. The brightness buttons do not show up in the
xev logs at all but this might be normal even if they work.
I'm getting suspicious of notify-osd as I'm not getting any notifications and running for example
notify-send Testing does nothing but time-out after 50 seconds