Oecumenius

And when he says that when the thousand years are ended, that is, when the Lord, having fulfilled the economy of his flesh, has returned to the heavens, the bonds of the spiritual powers will be loosed from the Devil, and again he will deceive the nations; for it has been said in what has been spoken before that the Lord's presence among men abolishes the activity of the Devil. …

Commentary on Revelation ↗

Augustine of Hippo

And therefore during these three years and a half the souls of those who were slain for His testimony, both those which formerly passed from the body and those which shall pass in that last persecution, shall reign with Him till the mortal world come to an end, and pass into that kingdom in which there shall be no death. …

The City of God, Book 20 ↗

Bede

And when the thousand years are completed, etc. He said completed as part of a whole, for he will be released such that three years and six months of the last struggle will remain. But besides this trope, it is rightly said that the time is finished. For such small remnants are not to be counted, since seven hundred and as many years as God wills are called an hour by the apostle.

Commentary on Revelation ↗