Earl M. Wunderli argues that "Alpha and Omega" in 3 Nephi 9:18 represents an anachronism in the Book of Mormon.
Earl M. Wunderli, An Imperfect Book: What the Book of Mormon Tells us About itself (Salt Lake City: Signature Books, 2013), 154
Interestingly, the New Testament term “Alpha and Omega” is used once in the Book of Mormon by Jesus when he says he is “Alpha and Omega, the beginning at the end” (3 Ne. 9:18). The phrase occurs twice in the Bible, both in the Apocalypse (Rev. 1:8; 21:6). It is puzzling to think of why Jesus would use a Greek term among the Nephites or in what manner they may have recorded it so that Joseph Smith thought to translate it as he did. Again, it at least shows discretion over vocabulary. The great defender of the Book of Mormon, Hugh Nibley, recognized this as an “apparent anachronism,” which he said was “the peculiar idiom of the ancient sectaries” and “notoriously bad Greek.” On the other hand, since it was “an accepted English expression we may view it,” he wrote, “as the best way of conveying the meaning of a certain Nephite expression to English readers.” Nibley continued with great erudition to explain aspects of the term but bypassed the question of why God would speak to Nephites in the language of ancient sectaries and in what Nibley considered “bad Greek.”