The scrum team has already completed an increment and the PO has marked it as done and delivered to the client. The Customer makes this Live. The scrum team has now moved to third or fourth sprint. The customer now finds some bugs/changes to the first increment and sends it back and asks them to work on that as a top priority as that is of an immense business value to the first increment released.
Now where and how does this get into the PBI and when does the Dev Team work upon this. If the PO and Dev team decide to start working on the bug/change request sent by the client, the current sprint goal might not be reached within the specific Sprint.