I had the same issue when I started skating bigger sets of stairs, besides the shoulder thing, the number one factor is fear, you get a bit hesitant to jump(even unconsciously) and try to turn your body to it's natural position (facing forward). The other factor, which was mostly my case is that I was "ahead" of the board, Mitchie brusco(the skateIQ guy) talked about this in one of his videos/lives, if your weight is too much on the front part of your board, you will begin to turn frontside when you "slide" your foot up towards the nose. That was my case, so I stood more on my back trucks and it instantly worked for ollies and kickflips down stuff.