edit: sbierwagen points out below that my comment is wrong, the source was pointed out, I just missed it.

> A worth to read article by [Mike Malone](https://medium.com/@betable/tifu-by-using-math-random-f1c308...) explains the problem with Math.random() in more detail.

Probably the source of the shuffle (though it was not mentioned, its visualisation was used) considering the old implementation had been there for about 6 years (and had been partially busted until a few weeks ago)