You have to install external refresh rate of the monitor to 120Hz or lower. But in-game refresh rate limit must be set to default. That means, you have to either lower your screen refresh rate to the 120Hz via windows settings on the desktop or you must use something like RTSS (Riva Tuner Statistics Server) which has included option to cap refresh rate of the monitor per application.

Again, in-game FPS cap must be DEFAULT! Not 120Hz!

After doing those steps you will be granted with consistent mouse movement with no occasional slowdowns.
Ask your questions if something isn't clear.

This fix was found on pcgamingwiki page. Tho, it doesn't says that it will fix mouse inconsistency. Said fix described as microstutters fix. Helps with mouse issue nevertheless.

I personally met a problem: i wasn't able to create new profile or use one of my profiles from cloud, saved from other PC.

The problem appeared to be in OneDrive (hot garbage)
Not only it moves all documents in cloud automatically but doing so makes it unable to most older games to read save/config data since there's no "Documents" or "My Documents" folder inside "UserName" folder

In short, i disabled "folder backup" via OneDrive (My Documents folder and everything else), moved My Documents folder with my save files from OneDrive folder to actual My Documents folder and then deleted OneDrive altogether.

After doing so, not only i was able to create new profile, but my previous profiles from cloud were in place too. I hope it can help someone.