Why do only certain Project Issues Move in to next Sprint and other's don't?

[Courtney]

I have multiple projects on one board, when I complete sprint and select to move unresolved issues into to next sprint, all but 1 project's issues move into next sprint. One project's issues scatter into the backlog. I cannot see anything configured differently between this and the other projects. Mostly default settings, Software type, etc. 

There are a few similar questions in the Community, but not exactly the same as this. Others included subtasks for example, but there are no subtasks in this particular project of mine.