Twice within the last 6 weeks I have been given a slip of paper when boarding the plane which changes my seat assignment, even though I had a boarding pass with my original seat assignment documented there. In both cases, I was given a "poorer" seat. In the first case, I was in business class with a seat assignment in the front cabin and was moved to a seat by the galley. In the second case, I had a premium economy seat and was moved to a seat in the back of the plane. I was given some vague excuse about an equipment change, but in both cases, my original seat was available on the airplane, but was given to someone else. Is anyone else experiencing this? I don't fly often enough to have status with Delta, and I'm wondering if my seat was given to someone with status.