Notification Center displays same message multiple times (hundreds)
Since upgrading to macOS Sierra, when the Notification Center receives a notification it displays correctly the message, but in the Center itself the same message is displayed multiple times (hundreds). For example, a notification from Facebook would appear once with an occurence x 400. I changed the display setting to Alert, and now it displays on the screen once, but in the Notification Center it is displayed many times (see image below).
Is this a setting or configuration problem, or a bug?
MacBook Pro with Retina display, macOS Sierra (10.12), 2.8 GHz Intel Core i5; 16 GB RAM