According to Dionysius of Alexandria, writing in the third century, there were two memorials of John in Ephesus, and he suggested that there might have been two famous Johns who had lived in the province of Asia (whom he identifies as the authors of the Gospel of John and the book of Revelation respectively) (apud Eusebius, Hist. eccl. 7.25.16).
Dionysius, a bishop of Alexandria, had reservations concerning the book of Revelation, and while he did not reject it outright, he did suggest that another John other than the Evangelist might have written it (7.25.7). While he couldn’t suggest any other John specifically, he did note that there were two memorials (μνήματα) associated with the name of John in Ephesus, suggesting to him that a second famous John might have resided in Asia (7.25.16).
Why were there two memorials in Ephesus?

Jerome relates that according to many people, both memorials were associated with the same John (Vir.9).
Robert Eisler has suggested that the two memorials correspond respectively to John’s original resting place and to the church to which his remains were later interred. He notes that a manuscript of the Acts of John seems reflect knowledge of such a transference.[1]
There was an ancient church dedicated to John which was already in ruins in the sixth century on account of its age (Procopius, De Aedificis 5.1.5–6). Later the basilica of St John was built on the site, which now also lies in ruins.
However, the original resting place of John was still remembered and honored as late as 1920, when the Greeks were expelled from the city.[2]
There is no literary evidence that two famous Johns lived in Ephesus, beyond Dionysius’ conjecture; and all earlier writers associated the same John with both the Gospel and Revelation.
Further Reading
For a discussion of Dionysius’ arguments for the separate authorship of John and Revelation, see here.
Footnotes
[1]. Eisler, Enigma, 125–26.
[2]. Eisler, Enigma, 126–27.