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It was brought up in Paltalk that the ante Nicene Fathers believed the "sons of God" referred to fallen angels in Genesis 6. This is mostly true, especially in the case of Tertullian. However, not ALL of them believed the sons of God were angels. For example, we have Sextus Julius Africanus who was a contemporary of Tertullian, unlike Tertullian he was familiar with the Biblical languages even Hebrew.
He is Julius' commentary on Genesis 6:
When men multiplied on the earth, the angels of heaven came together with the daughters of men. In some copies I found "the sons of God." What is meant by the Spirit, in my opinion, is that the descendants of Seth are called the sons of God on account of the righteous men and patriarchs who have sprung from him, even down to the Saviour Himself; but that the descendants of Cain are named the seed of men, as having nothing divine in them, on account of the wickedness of their race and the inequality of their nature, being a mixed people, and having stirred the indignation of God. But if it is thought that these refer to angels, we must take them to be those who deal with magic and jugglery, who taught the women the motions of the stars and the knowledge of things celestial, by whose power they conceived the giants as their children, by whom wickedness came to its height on the earth, until God decreed that the whole race of the living should perish in their impiety by the deluge.--Fragment 2, Extant Works of Julius Africanus
We see here that he follows in line with the standard interpretation of today, that the Sons of God are the Sons of Seth, and the daughters of men are from Cain.
St Ephraim the Syrian writing in the late 4th century says similar in regard to Genesis 6, this is important since St Ephraim's reading of the Scriptures follows traditional rabbinical reading, even at that time there were some rabbis that held to this interpretation, though even in Judaism the predominant reading was "sons of God" referred to the angels.
"He called the sons of Seth sons of God, those who, like sons of Seth, had been called "the righteous people of God." The beautiful daughters of men whom they saw were the daughters of Cain who adorned themselves and became a snare to the eyes of the sons of Seth. Then Moses, said, they took to wife such of them as they chose, because when they took them, they acted very haughtily over those whom they chose. A poor one would exalt himself over the wife of a rich man and an old man would sin with the one who was young. The ugliest of all would act arrogantly over the most beautiful.....The mighty men who were born were born to the feeble tribe of Cain and not to the mighty tribe of Seth. The house of Cain, because the earth had been cursed so as not to give them its strength, produced small harvests, deprived of its strength, just as it is today that some seeds, fruits, and grasses give strength and some do not. Because, at that time, they were cursed and sons of the cursed and were dwelling in the land of curses, they would gather and eat produced that lacked nutrition, and those who ate these were without strength just like the food that they ate. As for the Sethites, on the other hand, because they were the descendants of the blessed and were dwelling in the land along the boundary of the fence of Paradise, their produce was abundant and full of strength. So too were the bodies of those that ate that produce strong and powerful....After Moses spoke about the mighty men who were born into the tribe of Cain, whose women, even though beautiful, were nevertheless smaller than the sons of Seth...--Ephrem the Syrian, Commentary on Genesis page 135-136
Regardless how many early Christians read sons of God as the sons of Seth, is irrelevant, my point is simply to established that the Seth interpretation was not a post Nicene invention, but rather a preexistent, though less favored interpretation.
