I have heard that the source of the randiness in Catholicism is apostasy —and that apostasy is Arianism. But that’s only hearsay.
If so then Arianism is the same apostasy as that which unglues mainline protestant churches:
Arianism is the low view of Jesus: that he is not fully God. But rather just a man. Arianism became dominant in Europe in the protestant seminaries in the 1850’s by way of the “higher criticism” school and went on the kill off the protestant churches in Europe over the course of about 5 generations. Arianism byo “higher criticism” jumped the pond a half century later and became dominant in the American mainline protestant seminaries by 1930 or so—leading to the steady decline of all American mainline protestant denominations. (After all, why worship a dead guy and a human sacrifice at that.)
I don’t know if or how Arianism worked its way into the catholic church.
Which is why my Grandfather left Germany for Nebraska. He did not like the church union, and had no desire to fight for the Kaiser.