No dogmatic council can contradict another. The Council of Constance defined against the notion of loss of papal office due to sin, even publicly manifest scandal. Knowing this truth about the Catholic Faith, keep in mind that in 1415, an ecunemical Council condemns the following errors of the heretic John Hus:
"No one takes the place of Christ or of Peter unless he follows him in character, since no other succession is more important, and not otherwise does he receive from God the procuratorial power, because for that office of vicar are required both conformity in character and the authority of Him who institutes it".
"The pope is not the true and manifest successor of Peter, the first of the apostles, if he lives in a manner contrary to Peter; and if he be avaricious, then he is the vicar of Judas Iscariot. And with like evidence the cardinals are not the true and manifest successors of the college of the other apostles of Christ, unless they live in the manner of the apostles, keeping the commandments and counsels of our Lord Jesus Christ".
This means, that Pontiffs who are very evil are still validly elected popes.
When saints such as St. Robert Bellarmine or the Angelic Doctor wrote about a Pope being in error, even heresy, they agreed that we must resist, even publicly, if necessary. Bellarmine went so far as to propose that the Pontiff could lose his office: Note that he did not go further, telling us to leave or to make this declaration ourselves, declaring ourselves as the one true Church and condemning those who follow not.
Of course, each person is entitled to have his/her own opinion. But truth is sedevacantism will never be more than a theological opinion so it is best not to sucuмb to the temptation. Sedevacantism as an explanation to a heretic crisis is also a novelty. The concern here is about Faith purity, though.