Sorry for the lack of an answer, I just rediscovered this when going through the bug report topics.
So right now, we force a synchronization of the library with the file system when unloading the library to make sure everything is up-to-date before exiting. Normally this is not an issue, but when there is a large number of pending changes in the file system (which could be a big scanned folder that has just been added) this can make it seem like the application is hanging at the unloading stage.
Since we also had a performance issue in the scanning process in 1.0.0-rc.30 based on crash reports it seems like a few people were in a similar situation and had to force-quit the application. With the fix in 1.0.0-rc.31, this is now less of an issue, but it’s still there. As a proper solution, I would propose to let the application perform the synchronization for a bit (10 seconds maybe) and only then display a message/button that allows to skip the rest of the scanning process if desired.