As you know wyverns can be momentarily staggered if they take enough damage while rising to perform their divekick. however, this staggerable state is held during the divekick animation itself. As a result, if you stagger the wyvern during the divekick animation it will gain an absurd amount of momentum as it enters the stagger animation. If it knocks into you with this momentum you will automatically die due to the physics of it, which is obviously not the intent given the fact that it's the way to stop the divekick.