Hickory is my favorite wood. I cut and use a lot of shagbark here in VT, but also use bitternut and pignut occasionally.
Hickory is very dense, and requires a long time to dry and an even longer time to season well. You went from living tree to finished bow in 2 months in the summer, and unless you live in the middle of the desert or kept the wood in a hot box the whole time there's no way that wood was dry. Without seeing pics of your design my first guess is that your wood was still too wet when you tillered the bow, and you did irreparable damage to the limbs during tillering and doomed the bow to a life of sluggishness.