Previously, my done stories would disappear from the board after I start a new sprint but recently the done stories remain on the board after starting a new sprint.
How do I resolve this?
After the sprint completed, only the issues in the 'Cancel' column are removed and the issues in the 'done' column in the previous column reappear in the new sprint.
I think @Jack Brickey has already given you the answer.
For issues to be considered completed in a sprint they must be in the right-most column of the board.