The short version: People discovered that when doing certain activities, the game would lower your XP gained every time you completed the activity, but it would do so invisibly(IE the game would still display the same XP number, but you really only gained a portion of it). This wasn't just a glitch either, Bungie has put out a statement on it...
We’ve seen community discussion around XP gain in Destiny. After reviewing our data, we agree that the system is not performing the way we’d like it to. Today, we’d like to describe what’s going on under the hood, and talk about what you can expect going forward when it comes to earning XP in Destiny 2.
Currently, XP will scale up when playing longer or fixed duration activities like Crucible competitive multiplayer matches and the Leviathan Raid, and XP will scale down when playing activities that can be quickly, repeatedly chained, like grinding Public Events. We are not happy with the results, and we’ve heard the same from the community.
Effective immediately, we are deactivating this system.
As a result, players will see XP earn rates change for all activities across the board, but with all values being displayed consistently in the user interface. Over the course of the next week, we will be watching and reviewing XP game data to ensure that these changes meet our expectations, as well as yours. Any additional updates to this system will be communicated to you via our official channels.
Now, I've got no skin in the game for this one really, I haven't played either Destiny games, but I figured I would post this anyway since it seems very relevant in the wake of the backlash to Battlefront 2. I don't generally like systems like this that reduce XP, but I can't think of many off the top of my head(I know Payday 2 does it if you play the same heist over and over), but it's a totally valid design choice. Implementing this kind of system and making it hidden to the player though, seems rather poor. Now add in that system being interwoven with loot boxes that you can spend real money on is incredibly shady. Obviously I have no experience with these micro transactions, but even assuming they are the most benign loot boxes possible (which for comparison would probably be Overwatch's loot boxes) this is still 100% not okay.
Has anyone here spent real money on loot in Destiny 2, or felt like they've run up against this system?