Since gaming now lives at http://YouTube.com/gaming , the old Gaming app is going away on May 30th! If you were subscribed to channels in the Gaming app, they’ll automatically move to your YouTube subs feed on May 14th. More need-to-know info→ https://yt.be/help/yRe4
They came from the YouTube gaming app merge, I've already unsubscribed from most of them, I can't tell you who I've subscribed to myself but I have a few examples. Crainer Gaming, Jerome Ace, and Aphmau.