I was recently asked what amounts to: "When did Church Tradition go wrong?"
There are so many places in which the tradition to which RCC subscribes went wrong that it's impossible to place some collective When. There are also places where they still have it right - Trinity, Christology (kinda), Bible as God's Word (or, some RCs), etc.
So we would have to ask which doctrine in particular. And even then it's nearly impossible.
I invite you to consider three things:
1) How many churches in the NT already had it wrong? Even after apostolic teaching and even correction? Corinth, Rome, Galatia, Ephesus, Colossæ, Thessalonica, Crete, the church to which 1 John is addressed, Pergamum, Thyatira, Sardis, Laodicæa. And these are in the lifetime of the apostles!
And of course, the OT provides a paradigm for history as well - how much time did OT Israel spend in fairly-close obedience to God's Word? Very little. Yet God always preserved a remnant, which had the upper hand in numbers and influence sometimes but infrequently.
2) RCC picks and chooses which parts of CF writings it will follow and which it won't. The final authority is the Church. ECF writer X will say this or that and RCC will say "well, he's just speaking as a private theologian here", but if he says something else in the same document, alluvasudden he's a reliable witness to the universal and ancient church's constant tradition. Why should anyone put any credence in an approach such as that?
3) This is a subset of #2.
Theodoret of Cyrrhus (393-466) Hebrews 9:27-28: "As it is appointed for each human being to die once, and the one who accepts death’s decree no longer sins but awaits the examination of what was done in life, so Christ the Lord, after being offered once for us and taking up our sins, will come to us again, with sin no longer in force, that is, with sin no longer occupying a place as far as human beings are concerned. He said himself, remember, when he still had a mortal body, “He committed no sin, nor was guile found in his mouth.” It should be noted, of course, that he bore the sins of many, not of all: not all came to faith, so he removed the sins of the believers only." [Robert Charles Hill, Theodoret of Cyrus: Commentary on the Letters of St. Paul, Vol. 2 (Brookline: Holy Cross Orthodox Press, 2001), p. 175.
1st Epistle of Clement of Rome:
From him [arose] kings, princes, and rulers of the race of Judah. Nor are his other tribes in small glory, inasmuch as God had promised, "Thy seed shall be as the stars of heaven." All these, therefore, were highly honoured, and made great, not for their own sake, or for their own works, or for the righteousness which they wrought, but through the operation of His will. And we, too, being called by His will in Christ Jesus, are not justified by ourselves, nor by our own wisdom, or understanding, or godliness, or works which we have wrought in holiness of heart; but by that faith through which, from the beginning, Almighty God has justified all men. Amen
There are, then, of the Old Testament, twenty-two books in number; for, as I have heard, it is handed down that this is the number of the letters among the Hebrews...there are other books besides these not indeed included in the Canon, but appointed by the Fathers to be read by those who newly join us, and who wish for instruction in the word of godliness. The Wisdom of Solomon, and the Wisdom of Sirach, and Esther, and Judith, and Tobit" (Athanasius, Festal Letter 39:2-4, 39:7)
Let's just say for the sake of argument that Rome is right - Ath taught in more than one *other* place the opposite doctrine to what I've presented here. (And this happens all the time with all sorts of CFs.)
That leaves us w/ CFs who have contradicted themselves. To be consistent w/ these Ch Fathers (and remember, my claim is that modern RCC is inconsistent w/ them), RCC would either have to:
A: Teach just as inconsistently as these two guys do, sometimes saying one thing, sometimes the other, or
B: Call these teachings not actually part of Divine Tradition.
The problem w/ resolution A is that the cognitive dissonance would be pretty much unbearable. The upshot is that I don't know if I'd expect a lot of people to turn away from RCC in real life.
The thing about resolution B is that they have indeed already done just that. Somehow these two godly, forcible, powerful writers, from whom RCC ostensibly derives much of its tradition and doctrine, also produced impious, ungodly, and flat wrong teachings.
Now, how would the RC know this? Apparently from judging these non-"Apostolic Traditions" by... yup, you guessed it! What The Church® Says.
In the end, it's a vicious circle of question-begging. I claim the modern RCC is not totally faithful w/ Ch Fathers and then cite them when challenged. Then they say, "Hey, those aren't part of Apostolic Tradition!" I say, "Thanks for proving my point."
Note how this is the exact same thing they do with Scripture. Sola Ecclesia.
I also pause to note how pernicious this is. The Lord Jesus set an authoritative example for how one is to judge tradition - by Scripture. The RC refuses to do that and instead appeals to his own doctrinal construct which is already in place to then look BACK on tradition AND Scripture and pick and choose what he'll believe and what he won't believe. Thus the RC holds to the Scriptural teaching of the Deity of Christ and rejects the Scriptural teaching of salvation by grace alone thru faith alone. He accepts the Trinity and rejects sola scriptura. He accepts the fact that we should pray to God as commanded in the Scripture and rejects the fact that prayer to dead people and angels is strictly prohibited in the Scripture.
It becomes easy to see how this not only dishonors God in ideal (that is, that we should not judge men's teachings by God's) but also later in practice (bowing down to images, praying to dead people, trying to earn merit towards one's salvation).