My son was telling me the same thing, he says I told some guy 10 times to pass he would let me go. And then finally he says I cannot let you go.
I properly taught him how to fair warning to pass. at least 10 feet before the pass "rider on the left or right". I am sure he used the proper procedure but could not go through.
Well thats why there is cat3, thats how people learn. On the other hand riders should be considerate.
It makes a huge difference for young racers because they dont have the adult persistence and confidence to pursue passing. And adding some muddy and tight single tracks dont help it either. This was an experince for him and also for me. I will put mud tires before the muddy races too.