I just discovered that How do monster level and act number affect crowd control reduction? is a duplicate of How is CC reduced in higher difficulties?
This dup was earlier closed as a duplicate of a very broad question How do the different difficulty levels affect the gameplay? and iirc I was one of the close votes (since that was site policy to close narrow questions when subsumed by a broader context). Since then, we've had some discussion and decided against this approach, hence it was reopened later.
However, I am unable to cast a close vote on it - says that I have already voted to close, with 0 close votes shown there. Is this expected behavior or an SE bug?