Did the early Church Fathers have a complete agreement on how to interpret 1 Peter 3:18-20?

From the ACC doctrine: And this is attested by Ratzinger and the Church Fathers. Also modern Anglican theologians - the spirits were those who were drowned by God in the Great Flood of Noah. They were, so to speak, baptized by God, and then lifted up spiritually by the Spirit of the Son who "preached to them." Though the time interval between baptism and resurrection seems long to us, in eternal time it was the blink of an eye. The commentaries suggest that all were lifted up, and that prison is now empty. Though God condemned their behavior they were not "lost" for they had no knowledge of The Son of God, nor of the Abrahamic laws etc. so it wasn't their fault alone, God was partially responsible (he had no more patience) and so he baptized them and sent His Son to educate them, and offer salvation.

Not all the Fathers interpretations from the first few cents. have survived, so we don't know if they all had the same understanding. But since that understanding has appeared in various writings of Bishops since the 3rd. cent. until the current day, we can be pretty sure it was a wide held opinion of the Bishops.

Wicks, Jared. “Christ’s Saving Descent to the Dead: Early Witnesses from Ignatius of Antioch to Origen.” Pro Ecclesia 17, no. 3 (August 2008): 281–309. https://doi.org/10.1177/106385120801700303.

The article by Jared Wicks allows one to read the primary texts. He studies twelve texts before 180 CE and five texts from 180-300. This is very readable and easy to follow. This article can be found online and this will allow you to discovery the complexity of this issue. Here is my brief summary:

1. All the sources who cite 1 Pet 3:18-20 understand this to mean that Jesus preached his good news in Hades to those who were disobedient during the period when Noah was building the ark. The implied logic appears to be that this group did not have the benefit of a prophet; hence, Jesus offers them a “second chance” to attain salvation.

2. Nearly all of the Church Fathers have Jesus also preaching to the Jewish patriarchs and prophets. In so doing, Jesus acts in Hades with the same mandate that he had on earth, “Go only to the lost sheep of the House of Israel” (Matt 10:3).

3. Many emphasize that in the same way that Jesus opened up his apostles to a universal mission to the gentiles, it must be expected that Jesus preached to all the gentiles in Hades as well, going all the way back to Adam and Eve. Clement of Alexandria puts forward the principle that all humans are children of God; hence, just as the Church on earth is reaching out to all the nations, so, too, this same practice would apply to Hades. If Jesus does not do this himself, then it will be the practice of his apostles to do so after they die. This is a big step forward! Now it was not just Jesus but his apostles who were reaching out to the Gentiles while in Hades. Jesus was raised after three days, but the apostles continue their preaching mission for 2000 years.

4. In the third and following centuries, one can notice a gradual shift toward presenting Jesus as initiating violent action against the god Hades and tearing down the gates of his kingdom. Within this alteration, those who had enthusiastically accepted Jesus' message were enabled to join him in his ascension into heaven. Thus, this enabled the understanding that the saints were no longer "awaiting the resurrection in Hades," but they were passing through Hades and entering heaven shortly after their deaths.

5. Augustine decided that death had to be the deadline for determining a person’s salvation. Accordingly, Augustine reinterpreted 1 Pet 3:18-20 symbolically as referring to the future salvation that Jesus would bring to the human race. Likewise, Augustine identified "the spirits" as the humans living prior to the flood who were heralded to by the pre-existent Christ through the person of Noah.

An afterthought: Given the importance of Augustine in the West, Augustine effectively challanged all those who regarded Jesus' preaching as providing a "second chance" at salvation. Only in the Easter Orthodox Churches did the descent of Christ continue to shape their faith and their liturgy. During the Protestant Reformation, the descent of Christ into Hades was further challenged because, among Catholics, it was being used to support the practice of offering prayers and good works for the poor souls in Purgatory.

For further exploration: https://www.academia.edu/s/b56e1b238f

A note of caution:

In the last 120 years, the interpretation of the Sacred Scriptures has attained greater sophistication. When it comes to the interpretation of 1 Peter 3:18-20, the majority of scholars dedicated to 1 and 2 Peter have concluded that the Church Fathers appear to entirely misunderstood the text.

#1 The early Church Fathers entirely misunderstood the meaning of “spirits in prison” (1 Peter 3:19). From the second century to Augustine in the fifth century, the prevailing notion was that Jesus was actively preaching in Hades to those who had died during Noah’s flood. The “spirits in prison” consequently were the souls of those who died during the flood. But what would be the consequence if the early Church Fathers were absolutely mistaken in their exegesis of his foundational text? What if the “spirits in prison” actually referred to the fallen angels (referred to as “sons of God” in Gen 6:2, 4) who seduced the daughters of men and gave birth to “warriors of renown” (Gen 6:5)?

#2 This text is one of the most complex within the Scriptures. In 2019, by way of defining how the central meaning of this text, Campbell and van Rensburg were prompted to write this: “Few passages in the New Testament have caused greater scholarly deliberation and given rise to so many interpretations and counter-arguments than 1 Peter 3:18-22.”

#3 God did not spare the angels when they sinned, but cast them into TARTAROS (2 Peter 2:4). In the Greek Homeric tradition, Tartaros is the name of the deepest part of the Underworld where Greek gods were held captive and tormented. This was the perfect place where the God of Israel could confine and torment the angels of Gen 6:2-5.

#4 Who were the “spirits in prison” (ἐν φυλακῇ πνεύμασιν)? First, πνεύμασιν (spirits) in the plural is always in reference to angels in the New Testament. Second, it was common Jewish understanding that evil angels were imprisoned (cf. 1 En. 15:8; 21:1-10; Jub 5:6). Third, the interpretation that the disobedient angels in Gen. 6 were imprisoned “was standard in Peter’s day”.

#5 Here is a recent dissertation that can be found online.

Spirits and the Proclamation of Christ : 1 Peter 3:18-22 in its tradition-historical and literary context

Chad Pierce

Published 2009 Durham University PhD dissertation 278 Pages

1 Peter 3:18-22 records Christ’s proclamation to the “imprisoned spirits.” Interpreting this passage has challenged even the most competent exegetes. Earliest interpretations understood these imprisoned spirits as the souls of humans to whom Christ preached during his “harrowing of Hades” between his death and resurrection.

Scholars from the beginning of the twentieth century through the present have read these verses through the lens of the fall of the watchers (Gen 6:1-5) tradition first recorded in the Book of Watchers, thus reckoning these spirits as imprisoned angels. Yet contemporary scholarship has failed to acknowledge the development, conflation, and even multiplicity of the fallen angel sin and punishment myths that are found throughout much of early Jewish and Christian literature.

Fraternally,

Aaron Milavec

The conclusion of the Fathers is that these words mean the Descent into Hades. The Orthodox Icon depicts Christ raising the dead from beneath the earth (as our hymns say) which occurs eternally, that is, outside of time and at no particular time in relation to our understanding of time.

Thus, to answer your question:

1. The spirits are the dead from all time outside of Christ - who formerly didn't obey refers to the fall of Adam.
2. The prison is Hades, also known as Sheol, the place of the dead or the grave. The Psalmist calls it 'the Land of Forgetfulness'
3. The gospel, by which he raised them from the dead, or by which they were finally condemned, according to the disposition of their hearts as they were shaped by the deeds of their lives and their faith or lack thereof.

See: http://ancientfaith.com/podcasts/hopko/the_descent_of_jesus_into_hades

The only disagreement the Fathers seem to have is on who were the Spirits he preached to. However, Orthodox Tradition has come to understand that the 'formerly disobedient' refers even to those who have not yet died and will be outside of Christ. This is not universalism, but on the other hand does not condemn those outside of the Church outright.