They didn’t get as much extra experience points as they expected.
In the background, if you grind certain events (such as Public Events), Bungie‘s game limits the amount of XPs that you end up receiving. Regarding the situation, a detailed analysis surfaced on Reddit, and Bungie had to respond to it.
In short, they admit that the system doesn’t work as it was supposed to, and they are going to change it – in fact, it is getting shut down, and they will analyze in the last week of November to see if things are working normally. Players will get the amount of XP that is displayed on the screen.
The reason why it’s important is that Activision entered into a partnership with Kellogg’s in the United States (Pop-Tarts have a code to give you a 25% XP boost for four hours), and the players have made their voice heard… maybe they don’t get screwed now.