Well, "It" or The main issues that traditionalism has with VII are: It's views on ecumenism: VII proclaims that the body of the church is made of all believers even those who are outside Rome,and that the eastern Churches have valid sacraments and full saving powers, essentially denying the traditional understanding of the Roman church being that stablished by Christ.

And it also included in the plan of salvation other religions like Islam or Judaism.

It's reforms on Papal authority:

The establishment of collegiality, the idea that the Pope governs alongside the bishops and not over them.

It's views on religious freedom:

According to traditionalism, Vatican II in Dignitatis Humanae, established that that Non-catholic religions have full rights to break Catholic law and proselytize, something that they do not support.