There’s a pattern we sometimes find in citation and dispute. “Rav Yehuda cited Rav: X. And Shmuel says Y.” See for instance Chullin 57a. This either means
we have Rav’s X via Rav Yehuda, and Shmuel’s either directly or some unnamed intermediary
Rav Yehuda is teaching the controversy. After all, he studied from both Rav and Shmuel, so can cite both.
We have this pattern in Nedarim 45a:
דְּאָמַר רַבִּי יוֹחָנָן מִשּׁוּם רַבִּי שִׁמְעוֹן בֶּן יְהוֹצָדָק: כׇּל הַמַּפְקִיר בִּפְנֵי שְׁלֹשָׁה — הָוֵי הֶפְקֵר, בִּפְנֵי שְׁנַיִם — לָא הָוֵי הֶפְקֵר.
As Rabbi Yoḥanan said in the name of Rabbi Shimon ben Yehotzadak: With regard to anyone who declares an item ownerless before three people, that item is ownerless; if he does so before two people, it is not ownerless.
וְרַבִּי יְהוֹשֻׁעַ בֶּן לֵוִי אָמַר: דְּבַר תּוֹרָה אֲפִילּוּ בְּאֶחָד — הָוֵי הֶפְקֵר, וּמַה טַּעַם אָמְרוּ בִּשְׁלֹשָׁה, כְּדֵי שֶׁיְּהֵא אֶחָד זוֹכֶה וּשְׁנַיִם מְעִידִין.
And Rabbi Yehoshua ben Levi said: By Torah law, even with one person, the item is ownerless, and what is the reason that the Sages said that ownerless status must be declared with three people? It is so that one will take possession of the item and two will testify that the item was declared ownerless and that it was acquired by that person. It is not a requirement fundamental to the declaration of ownerless status.
Rabbi Shimon ben Yehotzadak (transitional Tanna / Amora generation) is earlier than Rabbi Yochanan. So is first-generation Amora, Rabbi Yehoshua ben Levi, who argues. (Although Rabbi Yochanan spans both first and second generations, he was much younger than the others in that generation, and belongs more to the second generation.) I believe Rabbi Yochanan cites both.
While those are the disputants in our printed texts and in Munich 95, there’s something interesting in the Vatican 110-111 manuscript. Rather than Rabbi Yehoshua ben Levi making the contrary statement, it is Rabbi Shimon ben Lakish:
The dispute would then be Rabbi Yochanan citing A saying X, and Reish Lakish saying Y. We have two second-generation Amoraim arguing.
I believe that Rabbi Yehoshua ben Levi is the correct reading. What caused the shift? First, dittography. We have had a run of Reish Lakish statements, on 44a and 44b, so he is to be expected, and can be מסיג גבול רעיהו. Further, the immediately preceding rabbi name was ר’ שמע’ בן followed by יהוצדק. (See image.) Here, at the end of the line, we have the identical words until בן, and then לקיש on the next line. Finally, there are shared letters in לוי and לקיש, namely the first letter of the patronymic, and יהושע and שמעון share the ש and the ע, potentially confusing the scribe.
But on top of all of this, I think, is the nagging aforementioned concern — who precisely is part of the citation or the dispute? Wouldn’t it be nicer if Rabbi Yochanan’s contemporary and student-colleague, Reish Lakish, would argue with him, rather than the messy ambiguity of Rabbi Yehoshua ben Levi appearing to (seemingly — not really) argue with Rabbi Yochanan?