Sometimes it's the back fibers separating from each other. Not like a splinter, more like a drying check or wind damage that doesn't appear until some stress is applied, especially after heat treat since more stress is out on the back. Those can be hard to find since they usually close up when the bow is unbraced. With those is jus yet open them up and full with super glue, then let it close back up. Sometimes I'll wrap them sometimes I don't
Kyle