I have the same issue. I noticed that in game my Dark Core Pro kept missing mouse clicks (really annoying in fps). So I tested clicking multiple browser tabs and again it missed some clicks. It would seem to missed 2 or 3 quick clicks in groups which is when I think it was freezing for a second or so. Changing to 500Hz, from 1000, seems to have helped. My dongle is in the rear of my K65 keyboard.