Second appeal decided on subject-matter jurisdiction

In M.E. v. Buncombe County Bd. of Educ., the Fourth Circuit in a per curiam opinion for the panel of Judges Widener, Williams, and Motz vacated the district court's decision following a prior appeal for lack of subject-matter jurisdiction, which makes me wonder where was that issue before the first appeal, but I guess subject-matter jurisdiction can never be waived or manufactured by the conduct of the parties.