Cannot connect to already running IDE instance. Exception: Process 464 is still running

Hi. The underlying issue was fixed in IDEA-330531, and the fix for it will should be available in versions 2023.3+.
 
As a workaround for your version, you can check to see what kind of process pid 525 is. If it is an IDEA process, kill it. If it's not an IDEA process, navigate to the IDE config folder and remove the .lock file in it.