St. Vincent Ferrer made mistakes, not only following the wrong Pope, but apparently he used to go around preaching that Judas repented and he was under fire by the Inquisition.
This is admittedly a minor point, but is there some official church pronouncement saying that Judas did not repent? It seems that, given the manner of his death, it would have been possible. Unlikely maybe, but possible. It may be an odd opinion to say he did, and I don't see any evidence for it in the gospels, but it surely isn't heresy, is it?