Bungie uncovers an issue in their distribution of random weapon perks in Destiny 2, detailed and interesting write up of the fix

Even for those that don't play Destiny 2, this is a super interesting look into "random" number generation. The background is that in Destiny 2, weapons drop with a "random" "column 3" (in the UI) perk and a "random" "column 4" perk, each from a pool of perks for that column. A weapon usually has 6 options for each column, so you can have 36 perk combinations per weapon. The community found that some specific combinations had drop rates noticeably lower than other perk combinations, which is what prompted Bungie to start investigate how their random number generation works.

This bug has been present since the Forsaken expansion (in 2018), but went largely unnoticed until now, when a new and heavily desired dungeon weapon has a clear god roll and that god roll was directly affected by this bug, resulting in abnormally low drop rates. This bug has been affecting weapons for up to 6 years, but was mostly on perk combos or on weapons that fewer people care about, so it wasn't noticed.

The TLDR is that their hashing algorithm was accidentally being fed sequential numbers, which resulted in a pattern in the distribution of the seeds generated, rather than being as random as it reasonably could be. As a fix, they're "salting" the data by multiplying the input by large prime numbers to ensure a more even distribution from the output.

I thought it was an extremely interesting writeup and somewhat unexpected for a game developer to give this much of a deep dive into a technical issue instead of just announcing they've fixed it with no further details.