I've very convinced that an author made a serious error in the main theorem in one of her 2012 papers in Statistics and Computing, which is a reputed journal in machine learning. I contacted the author, and we did have a respectful conversation, in which she neither agreed nor disagreed with me, but didn't seem to know a mathematically fundamental step mistakenly used in the proof of the theorem. Now, since I'm convinced that this is indeed a serious error, what should be my next step?
Along this line, I followed this question, and ideally I wanted to collaborate with the author, who did very kindly give me half an hour to discuss in real time, but I understand that there's no hope for writing a corrected version of the paper with her, since she neither agreed not disagreed with me.
Now since I'm in the beginning phase of my research career, I'm thinking of leveraging my discovery into writing a paper that'd be along the line of "Notes on the paper X", which'll mostly focus on discussing why the theorem and the proof is wrong. I do of course want to acknowledge the discussion with the author. How can I make this possible?
See the thing is: since the main theorem of the paper is wrong, it makes the subsequent experiments wrong as well, so I can't really do much to improve the results into something to make a brand new paper. However, I do want my contribution to the community (that catching the mistakes and explaining them why it's wrong with potential counterexamples) noted. This is the reason I want to publish my finding. Also I'm wondering even if I write to the editor, they acknowledge that it's a mistake, will they necessarily publish my notes in the same journal? Intuitive it seems no because it's just a correction (albeit to the main theorem), but yes, as this should be the appropriate choice, as this is the very journal the paper was published in. How should I go about it? Thank you!