Not able to earn hextech chests on 3v3

Hey, so I have noticed, that its not possible anymore to earn a hextech chest on the Twisted Treeline when you get a S- or higher, but I'm 100% sure that you normally could get hextech chests on 3v3 (the only thing you can't earn there are mastery tokens). Since I havn't read anything about in any recent patchnotes or in other news, I assume that this is a bug.