Dramatic League of Legends blue side win rate spike caused by bizarre bug, Riot says

In a Reddit post on the /r/leagueoflegends subreddit, user chocopouet detailed a lopsided winrate for blue side. According to their source, League of Graphs, blue side had a 55% winrate since the release of the 10 ban system. This is, of course, a big deal. Ideally, both sides should hover around the 50% area. Five extra percent may not seem like a lot, but when you consider the millions of League of Legends matches played a day, each number has a little more weight to it.

The post goes on the speculate reasons, considering that perhaps top laners are more OP than bot laners at the moment, which suggests that blue side is easier for top laners due to the gankability of their lane. Similarly, Rift Herald is easily accessible to blue side, so the user suggests that perhaps that could be the reason?

Riot Socrates, a League of Legends system designer, chimed in to the post, first claiming to be investigating the anomaly. He returned hours later with an explanation.

Alright we figured out what's up

tl;dr we goofed, and this bug was fixed yesterday

When we implemented 10 bans worldwide, there was a rare bug where sometimes you'd be assigned blue side then end up on red (and vice versa). We took a while to notice because our data audit also was reporting what it considered "healthy" side advantage (but in reality... wasn't) and it's skewed winrates on sites like League of Graphs. We caught this one yesterday so things should be getting back to normal now.

Turns out, the lopsided winrate wasn’t actually real at all. Instead, it was merely the result of a strange bug that listed and exported data incorrectly. Bizarre, but interesting. If this bug more heavily weighted blue side to red, then more wins were counting for blue, even when they should have been attributed to red. With this bug being fixed, we are already seeing a equalization of the sides on League of Graphs.