Pixels changing on import

I'm having pixel art created for a game I'm doing, but when I'm adding the files to the canvas in Photoshop, for whatever reason Photoshop is modifying the art and choosing what pixels to include/exclude. It's causing connecting pieces to not line-up and I'm not sure how to avoid it/correct for it. The image I've attached is from adding the same piece 5 times via drag/drop from Windows Explorer.