Dear Rabbi Kornfeld and colleagues,
Why is the plural sometimes spelled with a nun and sometimes with a mem in the very section that speaks of precise speech? Isn't this mixing Hebrew and Aramaic? What might be going on here?
Presumably, you are referring to the word on 53a "be'Yadan" which, in this very Sugya, is spelt sometimes with a 'Nun' and sometimes with a 'Mem'.
I have nothing concrete to offer you I'm afraid. The only suggestions I can think of is either that the Amora'im themselves were not particular about switching the two letters (in this particular format, since it makes not the least difference one way or the other), or that it is simply a printing error.
be'Virchas Kol Tuv