How do I remove duplicate apps shown in Notification Center?

Select the one you don't want and hit the delete key. Select both if you are not sure. They should be re-added the next time the app is installed.

Have your restarted your Mac to see if this helps?

Make sure you have a back up and proceed.

Open Terminal application and enter the following:

launchctl load -w /System/Library/LaunchAgents/com.apple.notificationcenterui.plist && killall NotificationCenter

Then try as I suggested before.

If the file is missing this is strange. If you have already tried restarting your Mac and the file is still not created then my next suggestion would be to do a System Reinstall over your existing system. That will reinstall any missing system files required for the Notification center.

This is what I did and this was my response. Did not work. I guess I should just forget it and leave them there for the time being.

This doesn't work. I tried it and it just does not delete. Is there another explanation?

When you select one app on the left side it should highlight. Then you press Delete on the keyboard. I just tried this and it works for me. I deleted every single one in Notification center.

I am in Sierra. Is that it won't work for me? It definitely doesn't work. I highlight it touch Delete and it is still there, two copies of the same app, laughing at me because I can't delete them.