If you've added a Works Order in the Load Orders screen, but it's not showing up when you press Start Production, there are several potential causes of this.
The first thing to check is if a duplicate order number has been added. The easiest way to verify this is to modify the problematic order number by adding the current date to it.
Example: Order 0001 becomes 0001-01012023
There are other causes of works orders not displaying, you can check it's Relased for Production Status, the Planning Location and if an order has been assigned to a user.