Re-reviewing a previously rejected article but some authors have changed from the previous submission. Should I mention that to the editor? I recently accepted to review an article for a journal. I actually reviewed the very same article for another journal from where the submission was rejected. This is a rather common occurrence however, as I was looking at my notes from the previous review to see if the authors have addressed the previous issues, I noticed that the new submission has actually different authors. For example:


Initial Submission: Author1, Author2, Author3, Author4, Author5 
New Submission: Author1, Author2, Author5, Author6, Author7


I will clearly mention in the review that I have reviewed the article before (actually the submission is in a different journal of the same publisher) but is the change of authors something that I should mention in my review?
It's not particularly unusual for authors to be added during a revision of a paper, but for them to be removed is quite unusual and often linked with something improper going on. 

Since this submission is a different publication than the original version that you saw, the editors do not have this history in front of them, and I think that it is indeed a good idea to flag this as a concern to the editors.

Moreover, if the article has not been significantly revised but the set of authors has changed, then that's a major red flag that the authors are doing something improper. If this is the case, then the editors absolutely must know, and should probably investigate wrongdoing.