Aside from that I agree with the other people that it’s almost impossible to imagine undergraduate students actually getting together as a group to screw over an instructor.

No, it happens. I have seen it. A group gets together, goes to their "academic" advisor to complain. This sets the mood in the classroom. No matter how much you try to be friendly or helpful, they will not let you in.

They just do not like you. They even say so in the evals. Why do they not like you? It is probably because they do not respect you. When you find a solution to this problem, especially for small youthful-looking female professionals, please write a book.