Without cutting the floor how can you ascertain the cause of the problem? Look at everything else relating to the job site. Using the metal bar tap test, tap on, around and across the underlament seams and listen for hollow spots. This will tell you if your underlayment is tight to the subfloor or if your floorcovering is not adhered to the underlayment. In most cases, unless you're very careful, while removing your sample (sandwich) you destroy the sample to the point where it is not representative of the problem.
Photo D shows what? An underlayment staple crown pushing upward or out; does this help you as you try to surmise the situation? If you are able go into the basement and look underneath your problem area. Sometimes you see what's going on a little clearer when you get a different angle.
Photo E shows what was visible from beneath, it's a great way to see the number of fasteners used both at the seams and in the field of the underlayment. But only if they are sticking through. But wait a minute, are the staples supposed to stick all the way through? And what kind of staples are they? Chisel points, which are recommended by underlayment manufacturers as an acceptable fastener, but is that the only one? No, divergent point (or saw tooth) fasteners are also recommended. I personally like divergent fasteners because what you see in Photo E and the close-up photo, Photo F, is less likely to happen, especially on an OSB type subfloor.