Hitting Cancel button causing the dialog box to disappear eventually, but not surprisingly, there is sometimes a java process that is orphaned and must be killed manually.

do you get the dialog about disconnecting or terminating when you exit?

Oh, I guess maybe it's that dialog that then proceeds to terminate, and that's what's getting stuck. I don't generally see that termination failing, but my context (OS and stuff) is different... maybe an experiment to test would be to start a fresh REPL and then exit and see if that terminates normally? That might provide some data as to whether the REPL process is not terminating nicely in general, or if it's maybe something that's running in the REPL which is slowing down its quitting process.

Happens to me infrequently but regularly. Even killing the java process doesn’t make the Terminating… window go away, and I sometimes must kill IntelliJ.