Turns out the author copied paragraphs of text verbatim from a separate project that I’m involved with and wrote the background for. Same text, same references, everything. The project details are not publicly available yet, so only the project team has had access to this document along with select reviewers. Additionally I found text copied from email correspondences that I had with a few team members in the manuscript and were portrayed as this individual’s commentary, so I’m pretty confident I know who this person is now.
To make things even more absurd, I previously reviewed a paper where the suspected individual was the lead author (was not blinded for that one) and noticed the background section was copied from another online resource. I let the editor know about this issue at the time and advised that the section be revised and cite back to the online resource. At the time I tried to give this person the benefit of the doubt so left it at that.