For some reasons (HNQ) I stumbled upon this question. I scrolled down, read through the answers and then I saw that there was no answer field:
This was strange, because the question seemed not to be closed, locked or protected. I reloaded the page and the issue persisted. Then I looked at the revision history and saw that the question was protected:
Now normally on protected questions I see a yellow banner either on the top or at the bottom of the page. So I went looking. I found these two questions:
Both questions are protected (as one can see from the revision history). For the first question (the meta one) I see the protection banner directly below the question.
On the latter question I saw nothing, so status-reproduced.
This is a bug. I can't answer a protected question due to low rep AND I don't see that it is protected.
I think this may be related to some clean-up work being done. Please revert this change.