Disclaimer: Not a developer, I just have quite a bit of experience with computers
This definitely seems like quite a strange bug, but here are some causes that I think are happening
1. Have you updated Osu! To the latest client/version. If so just update it
2. Do you have a slow/ Low-end/ damaged PC? I'm not saying get the highest end Pc that there is but a repair or a check may find some obstructions
3. Have you run any virus scans since this has started? There may be some viruses that cause unnecessary process executions, just run a thorough virus scan and it may go away.
Kind regards,
Alfexendor