You touch upon one of the biggest problems with SVism.  There's nothing in their position to serve as a principled backstop against simply declaring a Pope who teaches something they don't like to be an Anti-Pope.  Normally you come to the conclusion he's the Pope, and then if he teaches something (with the notes of infallibility) that contradicts your opinion, you then abandon your opinion and accept the new teaching with with the certainly of faith, which must be absolute and preclude even the slightest shadow of doubt.  Before Vatican I, for instance, many rejected papal infallibility, including a couple of approved Catechisms.  But then after the Council, most changed their view and accepted the teaching.  Some, the Old Catholics, persisted in rejecting it, and considered it heretical.  Well, an SV could have just declared Pius IX to be an Anti-Pope and could have written books akin to "Nikita Mastai-Ferretti", where they allege he was a Freemason.

In any case, no matter what any future pope teaches, could you ever truly have the absolute certainty of faith about it again?  Well, not if in the back of your head there this nagging little "what if .. ", as in "what if he's really an Anti-Pope and this teaching is heretical?".  That's an enormous problem with SVism, at least of the totalist variety.

With regard to the present Crisis, it's a huge problem for SVism that there's no evidence whatsoever that Montini had been a manifest heretic before he began teaching error at Vatican II.  Nada.  If someone were to uncover something at this point, it would be effectively so obscure that the heresy would have been occult rather than manifest.  Montini was an Archbishop, Roncalli a Cardinal, and nobody was calling them out for manifest heresy BEFORE V2 happened.

You really do need to have serious doubts PRIOR to when he starts teaching error.  If not, you must accept his teaching and conclude that you were in fact the one who had been in error.

Let's say we're 10 years into the reign of Pius XII.  No problems up to that point.  But then suddenly he teaches (with the notes of infallibility) something you consider to be grave error, if not heresy.  So you can now declare Pius XII an Anti-Pope and ... problem solved?  With those principles, no dogma is safe and no dogma can preclude some lingering shadow of doubt, since this guy could just be an Anti-Pope.  This is no less harmful to Catholic faith than R&R.  While SVs famously accuse R&R of Magisterium sifting, they can do the same thing, but take it a step further and engage in Pope-Sifting.  In both cases, their private judgment trumps the perceived teaching of a Pope and both put their private judgment as their ultimate rule of faith.

No, the answer must lie elsewhere.

You touch upon one of the biggest problems with SVism.  There's nothing in their position to serve as a principled backstop against simply declaring a Pope who teaches something they don't like to be an Anti-Pope.  Normally you come to the conclusion he's the Pope, and then if he teaches something (with the notes of infallibility) that contradicts your opinion, you then abandon your opinion and accept the new teaching with with the certainly of faith, which must be absolute and preclude even the slightest shadow of doubt.  Before Vatican I, for instance, many rejected papal infallibility, including a couple of approved Catechisms.  But then after the Council, most changed their view and accepted the teaching.  Some, the Old Catholics, persisted in rejecting it, and considered it heretical.  Well, an SV could have just declared Pius IX to be an Anti-Pope and could have written books akin to "Nikita Mastai-Ferretti", where they allege he was a Freemason.

In any case, no matter what any future pope teaches, could you ever truly have the absolute certainty of faith about it again?  Well, not if in the back of your head there this nagging little "what if .. ", as in "what if he's really an Anti-Pope and this teaching is heretical?".  That's an enormous problem with SVism, at least of the totalist variety.

With regard to the present Crisis, it's a huge problem for SVism that there's no evidence whatsoever that Montini had been a manifest heretic before he began teaching error at Vatican II.  Nada.  If someone were to uncover something at this point, it would be effectively so obscure that the heresy would have been occult rather than manifest.  Montini was an Archbishop, Roncalli a Cardinal, and nobody was calling them out for manifest heresy BEFORE V2 happened.

You really do need to have serious doubts PRIOR to when he starts teaching error.  If not, you must accept his teaching and conclude that you were in fact the one who had been in error.

Let's say we're 10 years into the reign of Pius XII.  No problems up to that point.  But then suddenly he teaches (with the notes of infallibility) something you consider to be grave error, if not heresy.  So you can now declare Pius XII an Anti-Pope and ... problem solved?  With those principles, no dogma is safe and no dogma can preclude some lingering shadow of doubt, since this guy could just be an Anti-Pope.  This is no less harmful to Catholic faith than R&R.  While SVs famously accuse R&R of Magisterium sifting, they can do the same thing, but take it a step further and engage in Pope-Sifting.  In both cases, their private judgment trumps the perceived teaching of a Pope and both put their private judgment as their ultimate rule of faith.

No, the answer must lie elsewhere.