During a kip, after you pull your legs to the bar you should be PULLING on the bar, this may be your problem. That is one reason why many coaches use the "pull up your pants" analogy.
The only bar skill that involves Pulling is a pull over. Every other skill involve pushing the bar to make your body go the direction opposite of the way you are pushing. If you pull on the bar during a kip, you will have bent arms and most likely won't make the skill. As soon as the word "pull" is used, the arms bend.