My understanding from a Microsoft ticket ,2311300040012741, is that resource capabilities will alter the resource to the best capacity in backward planning, but when neither resource achieves the ship date and it switches to forward planning, MRP will resort to the priority 1 machine without considering the priority 2 machine.

This means that even if priority 2 can achieve a better response in forward planning, priority 1 is choses.

We would love if planning optimization could also consider the secondary priority when forward planning.