In my experience, there is a serious issue with the Razer DeathAdder firmware updater.
Having a G15 keyboard plugged in while updating the hardware on your DeathAdder 3.5G may make your mouse power down and stop responding mid-process.
In my case it messed up the mouse to the point that Windows and the Razer drivers were unable to recognize it as a valid USB device.

At the same time, your G15 keyboard may also suffer damage, though so far I have only seen this issue affect the G15 LED Display.

I've had this problem happen twice on two different computers, both with a Logitech G15 v2 and Deathadder 3.5G.
I am not going to buy a 4th DA to confirm this further.