What should I do if a question has changed since I answered it? The other members vote my answer down because it actually doesn't answer the current question.
This kind of editing sometimes happens with chameleon questions where the OP keeps adding new questions, making my pre-existing answer now incomplete. But another pattern is when the OP asks an "XY problem" question, an answer points it out, and he changes the question to react to that. Those answers now not only aren't answers but can look very tangential to people who don't review the edit history.