The blue particles are copper sulphate. It was added years ago due to pressure from others regarding lack of copper in the formula. People have been noting the blue particles ever since. Nick mentioned years ago about uneven mixing causing the particles to be visible when you wouldn’t usually notice them.
I did a little research and question the need for it also. I would recommend shaking the bag vigorously to distribute the blue particles. Make sure the bag is zipped or you will have quite a mess.
My guess is that it takes a bit for copper sulfate to go into solution. If the formula is allowed to sit as per the recommendation, the copper sulfate should go into solution.