I took this morning 2 Wundrbar, one vanilla, one chocolate hazelnut, as I hesitated between which one I'd have for breakfast. I was struck by the difference in weight and size by holding them in my hands, so I weighted them.
Although it's written 100gr on the label for both flavours, the actual weight is very different: 87gr for the hazelnut one, 123gr for the vanilla one, both with the wrapper. Visually, it's also noticable when unpacked.
I took some pictures: http://imgur.com/a/TEQaA
You might want to have a call with the plant manager . I got them as part of the order #5087 made 2 weeks ago, if it can help you track the batch number.