I have a Dell XP 9570 i9 (HD) which I've only had for a couple of weeks. Apart from not waking from sleep which I've managed to cure I have terrible lag with my external USB keyboard and mouse. Initially I thought it might be the StarTech dock I was using but some testing has led me to believe it is a hardware/software issue with the Laptop.
The symptom is that as I type for a few seconds it will be fine and then it starts to lag and then it repeats keys. Eventually it settles down and then the issue starts again.
I have tried:
Keyboard plugged into a StarTech dock (I have 2 and have tried both).
Keyboard plugged into an old pluggable USB 2 hub which worked flawlessly for years with my old laptop.
Keyboard plugged directly into the Laptop - this seems to rule out the docks.
Two different keyboards - I have a wireless logitech at work and a wired QPad at home.
The StarTech dock is the USB3 one that allows 2 devices to share peripherals and display (KVM) and the other device I have attached is a small Dell PC and the keyboard works fine with that when plugged into the dock.
I have run Dell and Windows updates and updated everything including the BIOS (1.7.0).
I have disabled USB selective suspend in case it was that.
I have disabled Panel Self-Refresh in the Intel graphics control program as there some reports I found that suggested that as a possible culprit.
I'm not sure where else to go with this, but given that I know my docks work with other Laptops/PCs with the same keyboard(s) it MUST be related to the laptop software orhardware.
When you have access to important data a repeating delete key can be disasterous.