It appears totally broken to me, it might be the adblocker though (I also block social media): https://imgur.com/a/bB017 The same thing on Medium appears perfect without any social media link.
The first icon should be Twitter, so maybe it's really Adblocker. I've tested it with uBlock Origin and it shows the same behavior but, honestly, I don't want to tamper with that.
In fact, the sharers that are provided are meant to be examples, and not part of the core library. I guess simply changing the name attribute of the sharer would end up in showing the button.