Hello; I have a Dell XPS 9360. When I use the F1(mute)/F2(vol-)/F3(vol+), I also experience lag, but it only lags for the first bit (maybe a 1s lag). After it's "warmed up" all the keys are very responsive, until they cool down again.
You will also notice that the first time audio is played (usually a Windows 10 Notification), the notification appears much before the first sound appears (same lag). After the first "warm up" it'll be responsive again. I believe the issue is related to that, and there is no known fix for it. Once the "Audio Lag" issue is fixed, the responsivness of the keys will be normal as well.
There are a few big Audio issues with this XPS 9360.
Audio 1: Wave Service consumes 30% CPU when in a "Conversation" mode audio.
Audio 2: Small "Pop'ing" sounds happen when audio plays, usually 3 happen quickly, and 1 at the end.
Audio 3: The first audio is delayed (lag). (This is related to the responsive of the audio buttons as well).
And of course the Wifi Issues (and others):
Wifi: Killer Wireless crashes QCA8330 chipset routers (Archer C7 being the most popular), when transfering a large file over an internal network.
Touchpad: will often lag in chrome when chrome first starts, then becomes normal after a 2nd tab is opened.
The audio issue I'm sure will have to be a Driver update (either BIOS or AUDIO driver prob, or both). So will have to wait for that, if it ever happens. The Wifi also needs a driver update, but they have to be able to reproduce the issue first... so prob won't happen soon.
The laptop is great... but the Audio (and wifi a bit too) is terrible... very disapointed in the XPS 9360 Audio. There are things getting fixed though, there was huge issues with XPS9360 and Chrome browser playing videos. But Chrome fixed that. So things are coming along.