Dealing with potential plagiarism

I’m currently finishing up my PhD in a STEM field. A few years ago, I was the first author of a journal publication, for which I the lead researcher and did almost all of the writing for the manuscript. Since then, one of my then co-authors (another PhD student) on that article has published a separate paper on the same topic.

On reading this preprint, I found that several parts of the introduction were lifted verbatim from the introduction of my paper, or were added with lazy paraphrasing. When I saw this, I reached out to the colleague to express my concerns, and they said that any resemblance to my paper was “purely coincidental” and that they were willing to re-write the introduction.

However, once the final version was published, I found that the re-writing simply amounted to more paraphrasing, without any attempts to write an original introduction.

On one hand, the issue is mainly with the introduction, and not with the remaining content of the paper, so I’m inclined to not escalate the matter. On the other hand, this certainly goes against the journal’s plagiarism policy, and I do not appreciate my language and literature review being used without my consent.

Any advice on dealing with the situation is welcome.

Edit: Spelling and grammar