Not the IC. It appears in the 9th cent. and is condemned as a novelty in the following centuries.
There are a few ECF’s that believed in the IC before the 9th century.
Justin Martyr
[Jesus] became man by the Virgin so that the course that was taken by disobedience in the beginning through the agency of the serpent might be also the very course by which it would be put down. Eve, a virgin and undefiled, conceived the word of the serpent and bore disobedience and death. But the Virgin Mary received faith and joy when the angel Gabriel announced to her the glad tidings that the Spirit of the Lord would come upon her and the power of the Most High would overshadow her, for which reason the Holy One being born of her is the Son of God. And she replied, “Be it done unto me according to your word” (Luke 1:38) (Dialogue with Trypho 100 [A.D. 155]).
Irenaeus
Consequently, then, Mary the Virgin is found to be obedient, saying, “Behold, 0 Lord, your handmaid; be it done to me according to your word.” Eve . . . who was then still a virgin although she had Adam for a husband — for in paradise they were both naked but were not ashamed; for, having been created only a short time, they had no understanding of the procreation of children . . . having become disobedient [sin], was made the cause of death for herself and for the whole human race; so also Mary, betrothed to a man but nevertheless still a virgin, being obedient [no sin], was made the cause of salvation for herself and for the whole human race. . . . Thus, the knot of Eve’s disobedience was loosed by the obedience of Mary. What the virgin Eve had bound in unbelief, the Virgin Mary loosed through faith (Against Heresies 3:22:24 [A.D. 189]).
Origen
This Virgin Mother of the Only-begotten of God is called Mary, worthy of God, immaculate of the immaculate, one of the one (Homily 1 [A.D. 244]).
Hippolytus
He [Jesus] was the ark formed of incorruptible wood. For by this is signified that His tabernacle [Mary] was exempt from defilement and corruption (Orat. In Illud, Dominus pascit me, in Gallandi, Bibl. Patrum, II, 496 ante [A.D. 235]).
Ephraim the Syrian
You alone and your Mother are more beautiful than any others, for there is neither blemish in you nor any stains upon your Mother. Who of my children can compare in beauty to these? (Nisibene Hymns 27:8 [A. D. 361]).
Ambrose of Milan
Come, then, and search out your sheep, not through your servants or hired men, but do it yourself. Lift me up bodily and in the flesh, which is fallen in Adam. Lift me up not from Sarah but from Mary, a Virgin not only undefiled but a Virgin whom grace had made inviolate, free of every stain of sin (Commentary on Psalm 118:22-30 [A.D. 387]).
Gregory Nazianzen
He was conceived by the virgin, who had been first purified by the Spirit in soul and body; for, as it was fitting that childbearing should receive its share of honor, so it was necessary that virginity should receive even greater honor (Sermon 38 [d. A.D. 390]).
Augustine
We must except the Holy Virgin Mary, concerning whom I wish to raise no question when it touches the subject of sins, out of honor to the Lord; for from Him we know what abundance of grace for overcoming sin in every particular was conferred upon her who had the merit to conceive and bear Him who undoubtedly had no sin (Nature and Grace 36:42 [A.D. 415]).
Theodotus of Ancrya
A virgin, innocent, spotless, free of all defect, untouched, unsullied, holy in soul and body, like a lily sprouting among thorns (Homily 6:11[ante A.D. 446]).
Proclus of Constantinople
As He formed her without any stain of her own, so He proceeded from her contracting no stain (Homily 1[ante A.D. 446]).
Jacob of Sarug
[T]he very fact that God has elected her proves that none was ever holier than Mary, if any stain had disfigured her soul, if any other virgin had been purer and holier, God would have selected her and rejected Mary[ante A.D. 521].
Romanos the Melodist
Then the tribes of Israel heard that Anna had conceived the immaculate one. So everyone took part in the rejoicing. Joachim gave a banquet, and great was the merriment in the garden. He invited the priests and Levites to prayer; then he called Mary into the center of the crowd, that she might be magnified (On the Birth of Mary 1 [d. ca A.D. 560]).
Just because a few didn’t believe in the IC doesn’t mean that is wasn’t a widely held belief.
Besides, and correct me it I’m wrong but Bernard, Bonaventure, and Aquines were not ECF’s. It’s true that they are all doctor’s of the Church, but they held those beliefs before they were officially defined.
)