I was having an issue where the notifications were showing up for a second or two and went away as if no texts were received.  I was able to fix the issue by Disabling the Messaging+ application in Application Manager and then re-enabling it afterwards.   Notifications are working again. FYI, you should not lose anything by doing this as your texts and SMS messages are stored in the Phone Storage app, not Messaging+.  When you disable an app it will ask you if you want to delete all data and uninstall, but don't worry, nothing will be deleted.