Since upgrading to Sierra, every time I have a new notification (for instance Messages or Mail are the most common, but also Slack and other apps), I try to click on it but nothing happens. It used to close the notification and bring up the app, but now it doesn't do anything and it's really annoying; I have to manually switch to the app to see the message/act on it. Is this a bug, or by design? Anyone else has this issue?