Whether a reviewing court may affirm a conviction under plain error review based on speculation about the defendant's knowledge of his prohibited status, in the face of Rehaif errors that were not presented to the jury

QUESTION PRESENTED In a conviction for violation of 18 U.S.C. Section 922(g), after a jury trial held prior to this Court’s ruling in Rehaif v. United States, 139 S.Ct. 2191 (2019), wherein, contrary to Rehaif (1) neither the indictment’s charging language nor its factual allegations provided notice to the defendant that he would have to defend against the allegation that he knew his prohibited status, (2) the instructions to the jury erroneously omitted the essential element that the defendant knew he belonged to the relevant category of persons barred from possessing a firearm and the government was, thus, not put to its burden of proof, and (3) the omitted element was not contested at trial and, as a result, no evidence was presented regarding the defendant’s knowledge of his prohibited status, is it a violation of the defendant’s Fifth and Sixth Amendment rights for a reviewing court to affirm the conviction under plain error review on the basis that defendant’s substantial rights were not violated, a conclusion reached as the result of the reviewing court’s speculation that the government would be able to prove defendant’s knowledge of his prohibited status based on the defendant’s stipulation at trial that he was, in fact, a convicted felon, as well as based on the circumstances of the defendant’s prior felony noticed by the reviewing court but not presented to the jury, and to do so without regard to the cumulative effect of the Rehaif errors, all matters upon which there is a circuit conflict? ii