Nope, never saw any extra m. Sounds like something in your personal autocomplete "learned dictionary".
I don't know why, but 5 years ago the autocorrect on iOS never bothered me much, but over the past 1-2 years it's gotten much more "wrong". It's been driving me nuts.
To be clear, I don't have an iPhone myself, which is why I was wondering if you could check. I was referring to the video linked by the post. The phones there are brand new so they shouldn't have a learned dictionary, yet both the 2nd and third phone have the same behavior of adding an extra "m" at the end there if you look closely at the video.
I don't know why, but 5 years ago the autocorrect on iOS never bothered me much, but over the past 1-2 years it's gotten much more "wrong". It's been driving me nuts.