iPad pro background loses quality

I've had 2 certain backgrounds for YEARS. Tried to switch my lock screen background input and was pushed to change both backgrounds which irritated me. When I selected the photo option for the home screen, reselected the original picture I already had the quality dropped and there were terrible pixels around the edges of the subject in the image. But when I go through wallpaper history and go to my old combo it works... Same picture, different outcome. Come on Apple, we already are limited in customization please don't ruin our chances of wallpapers too.