How good is your Product Backlog Item prioritization?
Having a focused Sprint is an essential quality that a team and an organization must respect to a very high degree.
Adding and removing User Stories during the Sprint is a sign of suboptimal Product Owner's activities and the Team's ability to address dependencies at the Sprint Planning event.
Many non-green Sprints are also a sign the Scrum is not the best choice among all available agile methods, like Kanban, for example.
Improve planning sessions. Scope Change can reveal the team is not sharing knowledge or that there is not enough information available while ordering Product Backlog Items (PBIs), resulting in dropping an item during a current cycle and taking (and creating) a new PBI to satisfy some dependency.