Bue, I cant imagine that stabiil core, uniweft or any other glass type internal lam would make your particular design more stable. Nitty griity? weight the composite material against a maple composite and It may not be huge. I think the changes in the reverse taper and especially the longer riser(shorter working limb =less energy storage) were the culptits so maybe go a bit in the opposite direction. I wouldn't add anything in the core except maple if that is what you used. I think you have a really good design so build more with one change at a time and see what happens to performance.