Windows lags in idle for no reason

May 6, 2018
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My windows 10 custom build PC started lagging all of a sudden after a year of having no problem at all. Reinstall didn't help. At first it seemed to be something wrong with the mouse as it expressed itself as a lagging mouse cursor. Kinda like if you lag while playing a game, you fast forward when it loads up, the mouse cursor lagged the same, stopped while I was moving the mouse to a certain point and then warped all the way it was originally supposed to go.
Tried different mice too, same problem. Tried CPU/GPU/RAM stress tests, all passed. the only change I noticed was that it occurs just sometimes now. But when it does, it lags regularly for a certain period of time, at every single startup for a few minutes f.e., checked task manager to see if something takes any unusual load and found nothing, everything seemed normal.
Now how I realized it's not just mouse but rather the whole Windows. I played a video on YT and the video lagged along with the mouse except, surprisingly, for the sound, sound was just right, no fluctuations whatsoever.
I also tried to run games when I noticed it lags again, and for the most part, the games ran just fine, even with the problem being present while running it, no trouble. Just once in BF1 and ROTTR the bug showed itself in-game. Has anyone encountered a similar bug? And if so, what's the solution, or where does the problem come from? Is it possible that MOBO might be to blame?

My configuration:
CPU: AMD Ryzen 5 1600 @3,2GHz (no overclocking whatsoever)
GPU: ASUS DUAL RX580 8GB OC
MOBO: ASUS PRIME X370 PRO
RAM: Kingston HyperX FURY @2133MHz 4x4GB
PSU: EVOLVEO G650 80+Gold certified, modular
OS: Win10 pro installed on Samsung 960 EVO NVMe SSD
idle temps 30C-45C, load temps 45C-65C (73C for GPU under heavy load), except PCH, for some reason PCH sits between 65C-70C idle or not (common issue with my mobo as I’ve come to understand on the internet)