I don't think it was something as goofy as mentioning David Icke, for the record.
They completely wiped his channel and refunded subscribers. That's unprecedented. Plus, if you watch the video posted here of the last few minutes of his last stream, he looks at his phone and is visibly shaken up. His demeanor immediately changes and he looks like he's trying not to cry. You can hear him stifle sobs at some points.
Then he rambles about shit, including watching the documentary. Eventually it looks like he panicked and yelled "fuck" before ending the stream.
There are rumors of underaged girls, but all I've seen is like... thirdhand rumors. Other people who heard there are rumors. I feel like it's gotta be something big for Twitch to wipe his channel and NO ONE knows why.