Movement of underboard on EDPM roof

Maybe this is a common thing I don't need to worry about, but on one of the "seams" (from one side to the other) underneath my rubber roof, it feels like one of the boards (or whatever is under there) is loose. It pushes down when I walk on it (which I now try to avoid). It doesn't stick up enough (apparently) to damage the roof itself, but it definitely will at some point. I see no indication or any tear or weak spot in the roof.

You'll probably laugh at me, but my instincts are to drive a couple of short stainless screws down into it, then seal them with Dicor and Eternabond. Is that just a completely stupid idea?

I've also thought of running Eternabond all the way along that seam. It won't keep the board (or whatever) from moving, but at least it would lessen the chance of "wear" on the roof where that seam is.

Any thought are much appreciated.