It depends whether he/she is being naughty, feeling good or something is physically wrong and hurts when they jump. Putting trot rails on the landing side is a good way to maintain a horses focus and this should help to identify why they're kicking out. If they still do it with the rails, they're probably sore. Otherwise they're just messing around. The trot rails will also help with the cantering. Hope that helps

I think you should check their backs, because it can be something that interferes or hurt them. Good luck! 😊