I've never played with a tree hawk, but it sounds like there might be a bolster obstruction. Try running a wire or nipple pick, through the nipple and into the bolster. The turning the rifle to the side is knocking powder into the bolster under the nipple.

First thing I would do is make sure I had a stainless steel hot shot nipple. Second is take the nipple out of the rifle before you start your shooting for the day. Pour a few drops of isopropyl alcohol down the nipple threads into the bolster. If you have access to an air compresser, then blow some air through the bolster.

Another thing is change over to real black powder. That will help in the ignition of the rifle. Use 3f black powder. Also if you want to hunt with it, remove the nipple and put a pinch of black powder into the bolster and replace the nipple. This will also help insure that the rifle will go off. That small amount of powder in the bolster will send a bigger spark through the snail and make a hotter flame hit the breech.

If you still have troubles, do not be afraid to contact T/C. They are great with fixing things..