Kephapaulos,
' The letter Tuas Libenter' seems to be advising against bishops getting together in groups to discuss theological and other topics, to hold congresses, publish writings etc. This kind of activity, if these activities resulted in novel teachings being disseminated, could undermine the communion enjoyed between the pope and the bishops throughout the world. Pope Pius IX is being vigilant here.
On the other hand, the conciliar popes and the bishops speak with one voice on Vatican II.