In my understanding, your problem is weld line crack after annealing.
1.Increase MT should help,but this have deformation temperature limitation,I think you can try 110 degree C MT
2.Cracking issue have cavity No dependency as your description, so I think may be flow balance should be optimized.
3.I don't know the shape of this product,if the strength around current weld line place isn't strong enough, I am not sure if any possibility change gate position to move weld line.
4.At last, if appearance of this product is very strict required, there is way to make it better, "IHTC",Induction Heating Temperature Control.