That's all, folks!
They have more in common with the Old Catholics than that. Listen to what Pius XII wrote about where the first Old Catholic bishop received his episcopal consecration:
“But these men having progressed more boldly in the ways of wickedness and destruction, as happens to heretical sects from God’s just judgment, have wished to create a hierarchy also for themselves, as we have intimated. They have chosen and set up a pseudo-bishop, a certain notorious apostate from the Catholic faith, Joseph Hubert Reinkens. So that nothing be lacking in their impudence, for his consecration they have had refuge to those very Jansenists of Utrecht, whom they themselves, before they separated from the Church, considered as heretics and schismatics, as do all other Catholics. However, this Joseph Hubert dares to say that he is a bishop…”
The first Old Catholic bishop was consecrated by a Jansenist bishop, even though the Old Catholics themselves considered the Jansenists to be heretics and schismatics a few years earlier, before they split from the Church.
Where did the first sedevacantist bishop, Francis Schuckardt, founder of the CMRI, receive his episcopal consecration? He was ordained a priest and then consecrated bishop the next day by a married fallen away Catholics who had joined and immediately been consecrated bishop of - wait for it - the Old Catholic church!
I’ve said it before: the sedevacantists are nothing but the Old Catholics 2.0. The Old Catholics claim the Church – the Pope and all the bishops – defected at Vatican I. The sedevacantists say the Church – the Pope and all the bishops – defected at Vatican II. The first bishop of both sects received his episcopal consecration from a public heretic and schismatic, and both heresies use a false understanding of infallibility to "prove" that the indefectible Church defected.
The first sedevacantist bishop was eventually run out of the CMRI that he founded, when it was discovered that he was molesting his young male assistants and claiming to be Pope (Hadrian VII). The Antipope died in 2006, but unfortunately the movement he started and the sect he founded both live on.