To dream that you are trying to sit in your place, but it is already taken by someone else, means that you should be more curious and protective if you fish to save your dignity. The dream could also symbolize the unfair people or situations that you are surrounded by.
Dream dictionary: Line, losing your place in dream meanings
If you are waiting in the line and someone has taken from you, it shows that you think the life is not fair to you. The dream shows that the unfair friends or colleagues will try to take the advantage that was made to you.