When speedrunning MCPE, my friends couldn't hit the Ender Dragon at all while it was flying (not landing weirdly). We even went into Creative mode to test this, and most of our arrows were going through the dragon with very few actually landing a hit on it. This is most likely due to the Dragon having a different hitbox when flying around. This doesn't seem to be the case while it is landing as we could land every shot. Then we could hit it outside of the body with our swords, proving that there was a change in either hit identification or a change in hitbox size