More specifically, at the time when the TR was compiled the editor (Erasmus) had no Greek texts of RevJohn at hand, and being in a rush to complete his work before his competitor he just borrowed a very late Latin text to translate back into Greek.
The alternate text in the TR is so late that none of my apparatuses even acknowledge its existence (although my copy of Nestle-Aland does acknowledge a small set of variances later in the verse across eight texts and families including the Vulgate Latin generally in one case and the late Greek Orthodox Koine in the other, neither of which have anything to do with this variation–both are about adding a {tên timên} or “the honor/value” to “the glory of them” in a couple of different ways, the Vulgate version of which is unsurprisingly retained in the TR, too).
The structure of the sentence in actual Greek copies (and apparently in all surviving language copies until well after the 11th century) is quite different from the TR.
TR v.24:
kai ta ethnê tôn sôzomenôn en t(i)ô phôti autês peripatêsousi
and the nations of the saved in the light of her/it [the city] shall be walking (the lack of an ‘n’ at the end of the verb in Green’s TR is probably a typo)
All actual RevJohn texts (including the Vulgate translations not incidentally) up until they’re too late to be feasible witnesses to a possible original phraseology v.24:
kai peripatêsousin ta ethnê dia tou phôtos autês
and shall be walking the nations through/by the light of her/it
Unless there has been some kind of conspiracy to eliminate reference to this discrepancy in the pre-medieval texts both Western and Eastern (and I can’t figure out why there would be such a conspiracy), I am not remotely worried that the TR is a reconstruction of the original text at verse 24. Erasmus translated back into Greek from a very late Latin text he had at hand, and made a guess as to how it ran, and included a phrase not even found in the official post-schism Koine sets.