I have this exact same problem as well and have had it for the past few months. It only occurs in osu! and occurs no matter what peripheral I use, tried multiple mice and a Wacom drawing tablet set to pen mode. I have tried basically everything to solve it: system restore, reinstalling Windows, using default drivers for everything, killing all processes except for Osu and those necessary to run Windows,using onboard video and audio instead of my video and audio cards in case one of those had issues, etc.
I did not change any hardware since I first played this game, just one day when I tried playing I noticed this problem and have had it ever since. Presumably the problem came along with a new build of osu, but I'm not sure whether there was an update that day so it may have been another reason. It is absolutely infuriating to attempt to play this game with this bug since it essentially makes aiming properly impossible, and I have quit playing the game as a result since it just makes me frustrated like this. I do enjoy rhythm games very much, especially this one because of the active community and the huge library of beatmaps that is always growing. I find this game very fun and it has introduced me to a lot of music so I would be very thankful if I could get this issue resolved.
My PC specs, if it matters: