I think part of it is that in the first picture compared to the second picture there is a slight angling difference with your body. Also it might look different because in picture one the buttons are smoothed down to fit you body but while the other cosplayer is fixing them in picture two they are kind of ruffled and sticking up, perhaps conforming to a straighter line down the vest? I don't know.
About the third one, nearly everybody's belly seems to look better in front-shots than side-shots(including mine). When I stand in front of the mirror, my belly looks pretty much normal. But when I stand at my side(especially after heavy meals) it looks like I'm 5 months pregnant. But you're correct that you look significantly slimmer in the two latter photos. I'm not sure what else could be causing it if you've been maintaining your weight.