Wyclef and Hus, condemned proposition (Council of Constance):
"If the Pope is foreknown and evil, he does not have the power over the faithful given him by anyone, except perchance by Caesar"
Being foreknown and evil is something other than being a Public Heretic.
St Augustine divides people into the Categories Predestined and Foreknown. Unlike Calvin, he does not presume the Predestined know themselves to be such, nor any "once saved always saved" (state of grace now equalling a guarantee of not being among the foreknown) nor - unlike Wyclef and Hus - that the Foreknown will lose any kind of societal authority even in the Church by the fact of being foreknown or those out of grace momentarily momentarily lose any kind of societal right by being out of the state of grace until they repent.
Refusing to repent of one single mortal sin, even if it is a secret to the world, is being evil. If it continues to death, it implies being among the foreknown.
Excepting real acts of hasty judgement, it is impossible to know that someone is evil right now, except in very glaring circumstances, and even when it is clear someone is evil now, we cannot conclude with perfect certainty that he is among the foreknown. Maybe excepting a possible identification of the Apocalyptic False Prophet or the Apocalyptic Beast.
Valdensians went one further and denied also civil authority to the foreknown and evil, as well as the right of property.
If a Pope being a Public Heretic is supposed to be dealt with by the judgement of Constance about the quite different and possibly hidden situation that a Pope happens to be foreknown and evil, that is such a blatant confusion of categories.
And Robert Sungenis knows very well that his Patron Saint St Robert Bellarmine - a favourite for Sedisvacantists as well as for Geocentrics - did not make it. He had the Council of Constance and the other Councils up to Trent. And yet he says that a Pope if he ever should be a heretic, looses the Papacy by being such a heretic in a public fashion. He also stated that he did not think that would ever happen, unless I am misinformed.
What did he say about who you might be calling Antipope Felix II?
I read somewhere, but have not his works at hand, that when - I think it was Liberius signing the pseudo-creed of Sirmium - Pope Felix started to be Pope. Of course, you have his works, you can check the passage, it was maybe not a position he endorsed, I maybe got it wrong. He often cited several positions before giving his own, I do not have the passage at hand. But somehow I do not think he did lie. [Oops, sorry for the laughing matter, of course Saint Robert Bellarmine did not lie: but I do not think I misrecall either. Btw, Phil Plait was hilarious.]
The problem is that the horror previously felt for blatant heresy is now reserved for blatantly evil people - or people thought to be so.
In the mind of a modernist, the sentence against that proposition is equivalent to a similar sentence against the position of Saint Robert Bellarmine IF ever a Pope should be a heretic. I mean if someone poisoning innocent people (or possibly just shutting an eyelid about a daughter and a son doing so: if Alexander VI was maybe no poisoner, his children Lucrezia and Cesare pretty sure were) can remain Pope, why would anyone loose Papacy for such a trifle as signing the pseudo-creed of Sirmium?
Well, the possible poisoning of innocent people or the probable neglect of his children's morals - maybe he was not neglecting it but shunning them after all - are not a problem for Church men obeying his Papal orders. These are not acts he requires from anyone as Pope, only acts of which he is or possibly even is not personally guilty. But when a Pope makes a heresy into a public statement (even if not a Church law), he is after all endorsing that others take the Church law forbidding all heresy at least as allowing the in fact Heretical proposition of such a Pope, if ever such a thing should be the case.
Cum Ex Apostolatus says that everyone who ever even has been heretic before promotion to an office - including civil ones, like Emperor, King, Duke, Count, Baron (one can possibly interpret, though I do not know it as a statement: as long as the mass of the subjects are supposed to be Catholics) - is deposed automatically as soon as the fact becomes public and obeying such a man is a sin.
PS, I did on September 10th this year in Versailles dishonour my signature by signing a statement to the police which an officer had written out and it contained an error, which I was too tired to react against. But it was not an error against the faith, it was a misunderstanding on his part of what I had been telling him. He had, sadly enough, denied me the right to write my declaration myself before signing it.
PPS, in this kind of "equivalency" - as above between condemning Wyclef/Hus and what Sungenis is upbraiding the Sedisvacantism of Lane for - it is easy for Protestants like "Rev" Blakeney to write that St Alphonsus endorsed things like being ashamed of Christ before men, when in fact he did not. It is easy to make any statement equivalent to any other statement if there is only one term different - even if that term is sufficient to make a difference as between Heaven and Hell. I regret to say that some Sedisvacantist accusations against such and such a Pope also suffer from this kind of grammatical imprecision.