I'm using Windows 10 Professional on a desktop PC. At exactly 0 and 30 minutes of each hour the whole system stutters and lags for a moment. I.e. every half hour. Looks like this: each window gets a focus briefly, gets redrawn (blinks white), and after a few seconds it's all back to normal. If I type while it's happening, keystrokes are lost.
What might be the cause? It happens even if I just open a Notepad and do nothing.
I've also tried adjusting the clock to 59 or 29 minutes; sometimes the same strange things happens at the next "fake" 0/30 minutes, sometimes it does not.