I don't have any examples personally, but I've been told by a lot of people that he has some views about women, race, sex, homosexuality, etc which many would find objectionable.

Edit: his Twitter is pretty much 50% programming, 50% GOP politics. He might be a bit more progressive than your average Republican, but he still expresses a strong anti-left/anti-"woke" set of beliefs.

twitter happened, I guess

But today I stumbled across a long twitter thread that I can only describe as intentional character assassination. The author of this thread is misrepresenting facts and making some pretty nasty accusations. Again this is not all that unusual, except for the fact that I was not invited to defend myself. [...] The gist of this author’s thread is that I am a misogynist; and that I should not be taken seriously in any regard. I understand that efforts have been made to have me excluded from conferences, and to boycott the publisher of my books, etc.

- Uncle Bob in 2017

source and context