Ink sacs that are purchased from Wandering Traders aren't able to be used in crafting black glass, glass panes, concrete, terracota or wool. They also can't be crafted into black dye, and some items appear in the crafting table as needing ink sacs, although even if you have the items and the ink sacs, it will not let you craft that item. I can verify that this glitch affects both iOS and Xbox One versions.