It’s believed that the AC breed has extra melanizers not found on Silkies, these extra melanizers have yet to be studied so if I had to speculate is that some of your lines are lacking one or more of these melanizers.
There are many genes antagonistic to Fibromelanosis, Sex linked dominant Dermal Inhibitor(Id) is the most powerful, Barring, dominant white to a lesser degree, but it appears that on your case you must be missing melanizers instead of inhibitors, the leakage on the males feathers is due to loss...