Does the court have an obligation to determine whether subject matter jurisdiction exists as a preliminary matter?

QUESTION(S) PRESENTED If subject matter jurisdiction does not affirmatively appear in the record, is the judgement valid? Does the court have an obligation to determine whether subject matter jurisdiction exists as a preliminary matter when a motion to dismiss for lack of jurisdiction is timely filed pursuant to Fed.R.Crim.P. 12(B)(2)? Where the lower courts have failed to rule on the merits of a motion to dismiss for lack of jurisdiction pursuant to Federal Rule of Criminal Procedure 12(B)(2) can defendant's conviction be affirmed by the Court of Appeals? And has the defendant : been deprived of his due process under the Sixth Amendment of the United States! Constitution? i. Are motions filed while the case is still pending to dismiss for lack of subject matter jurisdiction barred by the mandate rule? Where a defendant timely files a motion to dismiss for lack of subject matter jurisdiction and the court fails to rule on the merits of said motion and subsequently enters a judgement against the defendant after jury trial has the defendant's right to a fair trial been violated?