I cannot be sure from your picture of the black bamboo, but it looks to me like what we call "poppyseed" bamboo. In the past I have harvested all my bamboo from a stand of Madake bamboo ,used for making Yumi's, and bamboo composite bows. Amongst the culms, there were some which had a fungus growing on it, which looked like poppy seed. It is a valued material for making special bows, but only used on the belly side. It is not good in tension. Your black bamboo could be a different variety, as there are so many varieties of bamboo. There are also many other factors which could cause the bamboo to lift like that. Moisture content, how the bamboo was dried ( in a kiln vs. slowly drying in the sun over months) and how thick the backing is on your bow. I prefer to make mine as thin as I can, and take it to knife edge thickness when gluing to the back of the bow. Your bow is beautiful and I really like the combo of purpleheart and osage. Creative way to save the bow. Best wishes.