The Gemoro on 147b says in one place that our Mishnah is Reb Shimon, but in another place that our Mishnah is not like Reb Shimon.
Obviously this is strange, but also the Gemoro did not even notice this and ask. We do find occasionaly that different parts of a Stam Mishnah are different Tanaim, or that the Mishnah could be Rebbi who holds like one Tana for one Halocho and another Tana for another Halochoh, but here the Gemoro doesn't ask this.
I wonder if you have any comments Thanks
Here, we cannot ask that there is a contradiction between Stam Mishnayos, because the Mishnayos to which the Gemara is referring are in two different Masechtos and are not connect to each other at all. Furthermore, Tosfos (DH Ein Mashkin) writes that there is, in truth, no real contradiction between the Mishnayos and they can be easily resolved with one another.
Even at the beginning of Maseches Beitzah, when the Gemara says regarding a Stam Mishnah that "Rebbi taught us Mishnayos from two differing Tana'im," the Gemara does not ask from one Mishnah to another in the form of a question and answer. Rather, it mentions this idea in order to explain the ruling of Rav Nachman, who follows the opinion of Rebbi Yehudah only on Yom Tov. The Gemara brings Stam Mishnayos as proof for this.
Our apologies for the delay in responding to your question.