Disclosure.
The person named in the Acknowledgements section of the article wrote to the editor stating that he or she was partially responsible for the analysis and interpretation of the data and should therefore be named as an author.
From the editor's reading of the correspondence between the authors, it seems that the main author used the ideas of the "complainant" to some extent, in that the published paper does indeed take one of the lines of interpretation that the complainant suggested (a line of interpretation that was not given due importance in the first draft of the manuscript from the author that was originally provided to the complainant and that I have seen). The analysis presented in the published paper differed slightly, but not significantly, from the analysis that the complainant had performed earlier. The author insists that none of these points is correct and that the complainant did not play any role in shaping the article, but rather suggested a different focus of the analysis/article that they had not considered.
The editor has not been able to reach an agreement between the two parties and cannot reconcile their two separate opinions on what happened over time, including the claims that some of the emails pasted into the Word documents were altered. Thus, the editor cannot confidently reject or accept the complaint.
COPE's advice.
This is essentially a dispute over authorship, and the editor cannot be expected to rule on the matter. It is not the role of editors to resolve authorship disputes. An article should not be retracted. But the editor can publish a notice of disputed authorship. The advice was to write to the complainant, explaining that this is a matter between them and the author and that the complainant should contact the author's institution if they wish to do so. In the future, it may be useful for editors to confirm that those named in acknowledgements are aware of this fact and agree to the inclusion.
Source: https://entc.com.ua/uk/1970-mene-vyznaly-ale-ia-povynen-buty-avtorom