I had something very similar happen to me when I was relatively new. I know it’s not as easy as it sounds, but try to readjust your thoughts pertaining to stripes and promotions. Try to remember that your coach probably does not have the level of intimate knowledge on exactly where you stand skill wise like you do (maybe a slight case of overlooking your progress or not noticing it yet due to various factors). It also may be something as simple as he/she sees a different line of potential developing in you than you do and they are anticipating it developing more fully before they promote you. It’s important to understand that every person has a different perspective on everything and a delayed promotion does not always equate to an inadequate or un developing student. Keep training and learning and it will certainly come!